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 $58.32   4.787%   $61.1118   $61.11   $61.10   $61.10  
  Purchase #2 $82.32   13.317%   $93.2826   $93.28   $93.30   $93.30  
  Purchase #3 $74.95   7.474%   $80.5518   $80.55   $80.55   $80.60  
  Purchase #4 $102.44   9.596%   $112.2701   $112.27   $112.25   $112.30  
  Purchase #5 $189.54   6.278%   $201.4393   $201.44   $201.45   $201.40  
  Purchase #6 $222.75   8.867%   $242.5012   $242.50   $242.50   $242.50  
  Purchase #7 $105.95   12.747%   $119.4554   $119.46   $119.45   $119.50  
  7 purchase totals = $836.27       $910.6122   $910.61   $910.60   $910.70