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 $93.52   11.454%   $104.2318   $104.23   $104.25   $104.20  
  Purchase #2 $176.59   10.396%   $194.9483   $194.95   $194.95   $194.90  
  Purchase #3 $33.51   4.589%   $35.0478   $35.05   $35.05   $35.00  
  Purchase #4 $48.39   9.379%   $52.9285   $52.93   $52.95   $52.90  
  Purchase #5 $170.30   10.756%   $188.6175   $188.62   $188.60   $188.60  
  Purchase #6 $181.37   11.123%   $201.5438   $201.54   $201.55   $201.50  
  Purchase #7 $247.42   6.677%   $263.9402   $263.94   $263.95   $263.90  
  7 purchase totals = $951.10       $1,041.2579   $1,041.26   $1,041.30   $1,041.00