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 $87.68   11.221%   $97.5186   $97.52   $97.50   $97.50  
  Purchase #2 $238.79   10.770%   $264.5077   $264.51   $264.50   $264.50  
  Purchase #3 $225.96   13.794%   $257.1289   $257.13   $257.15   $257.10  
  Purchase #4 $188.53   11.637%   $210.4692   $210.47   $210.45   $210.50  
  Purchase #5 $199.70   4.533%   $208.7524   $208.75   $208.75   $208.80  
  Purchase #6 $117.56   11.621%   $131.2216   $131.22   $131.20   $131.20  
  Purchase #7 $79.98   6.712%   $85.3483   $85.35   $85.35   $85.30  
  7 purchase totals = $1,138.20       $1,254.9467   $1,254.95   $1,254.90   $1,254.90