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 $54.98   8.112%   $59.44   $59.44   $59.45   $59.40  
  Purchase #2 $113.99   7.143%   $122.1323   $122.13   $122.15   $122.10  
  Purchase #3 $209.66   13.750%   $238.4883   $238.49   $238.50   $238.50  
  Purchase #4 $170.29   7.313%   $182.7433   $182.74   $182.75   $182.70  
  Purchase #5 $163.61   9.162%   $178.5999   $178.60   $178.60   $178.60  
  Purchase #6 $119.57   13.710%   $135.963   $135.96   $135.95   $136.00  
  Purchase #7 $120.75   13.739%   $137.3398   $137.34   $137.35   $137.30  
  7 purchase totals = $952.85       $1,054.7066   $1,054.70   $1,054.75   $1,054.60