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 $49.58   13.454%   $56.2505   $56.25   $56.25   $56.30  
  Purchase #2 $110.89   10.633%   $122.6809   $122.68   $122.70   $122.70  
  Purchase #3 $59.29   6.755%   $63.295   $63.30   $63.30   $63.30  
  Purchase #4 $113.43   8.537%   $123.1135   $123.11   $123.10   $123.10  
  Purchase #5 $30.67   3.800%   $31.8355   $31.84   $31.85   $31.80  
  Purchase #6 $119.25   3.374%   $123.2735   $123.27   $123.25   $123.30  
  Purchase #7 $202.50   4.444%   $211.4991   $211.50   $211.50   $211.50  
  7 purchase totals = $685.61       $731.9480   $731.95   $731.95   $732.00