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 $70.39   8.545%   $76.4048   $76.40   $76.40   $76.40  
  Purchase #2 $93.54   12.191%   $104.9435   $104.94   $104.95   $104.90  
  Purchase #3 $150.89   8.770%   $164.1231   $164.12   $164.10   $164.10  
  Purchase #4 $211.33   13.177%   $239.177   $239.18   $239.20   $239.20  
  Purchase #5 $164.49   11.102%   $182.7517   $182.75   $182.75   $182.80  
  Purchase #6 $138.71   5.719%   $146.6428   $146.64   $146.65   $146.60  
  Purchase #7 $236.39   13.157%   $267.4918   $267.49   $267.50   $267.50  
  7 purchase totals = $1,065.74       $1,181.5347   $1,181.52   $1,181.55   $1,181.50