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 $42.57   6.453%   $45.317   $45.32   $45.30   $45.30  
  Purchase #2 $191.28   12.743%   $215.6548   $215.65   $215.65   $215.70  
  Purchase #3 $52.90   3.792%   $54.906   $54.91   $54.90   $54.90  
  Purchase #4 $201.33   5.180%   $211.7589   $211.76   $211.75   $211.80  
  Purchase #5 $119.94   5.787%   $126.8809   $126.88   $126.90   $126.90  
  Purchase #6 $93.35   11.597%   $104.1758   $104.18   $104.20   $104.20  
  Purchase #7 $200.64   4.270%   $209.2073   $209.21   $209.20   $209.20  
  7 purchase totals = $902.01       $967.9007   $967.91   $967.90   $968.00