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 $63.32   4.579%   $66.2194   $66.22   $66.20   $66.20  
  Purchase #2 $6.48   3.650%   $6.7165   $6.72   $6.70   $6.70  
  Purchase #3 $188.72   7.319%   $202.5324   $202.53   $202.55   $202.50  
  Purchase #4 $52.58   5.363%   $55.3999   $55.40   $55.40   $55.40  
  Purchase #5 $163.70   7.457%   $175.9071   $175.91   $175.90   $175.90  
  Purchase #6 $151.88   4.252%   $158.3379   $158.34   $158.35   $158.30  
  Purchase #7 $149.78   6.836%   $160.019   $160.02   $160.00   $160.00  
  7 purchase totals = $776.46       $825.1322   $825.14   $825.10   $825.00