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 $232.82   5.798%   $246.3189   $246.32   $246.30   $246.30  
  Purchase #2 $114.80   11.273%   $127.7414   $127.74   $127.75   $127.70  
  Purchase #3 $205.50   10.173%   $226.4055   $226.41   $226.40   $226.40  
  Purchase #4 $173.68   5.424%   $183.1004   $183.10   $183.10   $183.10  
  Purchase #5 $159.88   6.482%   $170.2434   $170.24   $170.25   $170.20  
  Purchase #6 $61.78   6.312%   $65.6796   $65.68   $65.70   $65.70  
  Purchase #7 $174.66   3.272%   $180.3749   $180.37   $180.35   $180.40  
  7 purchase totals = $1,123.12       $1,199.8641   $1,199.86   $1,199.85   $1,199.80