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 $208.82   13.487%   $236.9836   $236.98   $237.00   $237.00  
  Purchase #2 $67.91   7.252%   $72.8348   $72.83   $72.85   $72.80  
  Purchase #3 $162.80   11.138%   $180.9327   $180.93   $180.95   $180.90  
  Purchase #4 $33.37   13.187%   $37.7705   $37.77   $37.75   $37.80  
  Purchase #5 $108.39   9.654%   $118.854   $118.85   $118.85   $118.90  
  Purchase #6 $167.93   4.562%   $175.591   $175.59   $175.60   $175.60  
  Purchase #7 $60.72   12.336%   $68.2104   $68.21   $68.20   $68.20  
  7 purchase totals = $809.94       $891.1770   $891.16   $891.20   $891.20