Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $173.72   13.462%   $197.1062   $197.11   $197.10   $197.10  
  Purchase #2 $147.95   6.516%   $157.5904   $157.59   $157.60   $157.60  
  Purchase #3 $101.82   12.734%   $114.7858   $114.79   $114.80   $114.80  
  Purchase #4 $127.99   11.762%   $143.0442   $143.04   $143.05   $143.00  
  Purchase #5 $180.76   13.773%   $205.6561   $205.66   $205.65   $205.70  
  Purchase #6 $219.47   3.335%   $226.7893   $226.79   $226.80   $226.80  
  Purchase #7 $105.87   4.765%   $110.9147   $110.91   $110.90   $110.90  
  7 purchase totals = $1,057.58       $1,155.8867   $1,155.89   $1,155.90   $1,155.90