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 $83.52   11.636%   $93.2384   $93.24   $93.25   $93.20  
  Purchase #2 $210.58   11.383%   $234.5503   $234.55   $234.55   $234.60  
  Purchase #3 $117.76   13.331%   $133.4586   $133.46   $133.45   $133.50  
  Purchase #4 $152.96   6.731%   $163.2557   $163.26   $163.25   $163.30  
  Purchase #5 $86.55   5.413%   $91.235   $91.24   $91.25   $91.20  
  Purchase #6 $14.45   3.175%   $14.9088   $14.91   $14.90   $14.90  
  Purchase #7 $250.43   5.722%   $264.7596   $264.76   $264.75   $264.80  
  7 purchase totals = $916.25       $995.4064   $995.42   $995.40   $995.50