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 $191.96   6.201%   $203.8634   $203.86   $203.85   $203.90  
  Purchase #2 $58.33   5.740%   $61.6781   $61.68   $61.70   $61.70  
  Purchase #3 $209.52   11.134%   $232.848   $232.85   $232.85   $232.80  
  Purchase #4 $33.63   4.213%   $35.0468   $35.05   $35.05   $35.00  
  Purchase #5 $122.57   3.228%   $126.5266   $126.53   $126.55   $126.50  
  Purchase #6 $201.61   3.826%   $209.3236   $209.32   $209.30   $209.30  
  Purchase #7 $104.86   11.372%   $116.7847   $116.78   $116.80   $116.80  
  7 purchase totals = $922.48       $986.0712   $986.07   $986.10   $986.00