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 $203.86   13.359%   $231.0937   $231.09   $231.10   $231.10  
  Purchase #2 $250.54   9.804%   $275.1029   $275.10   $275.10   $275.10  
  Purchase #3 $62.63   7.229%   $67.1575   $67.16   $67.15   $67.20  
  Purchase #4 $188.35   4.265%   $196.3831   $196.38   $196.40   $196.40  
  Purchase #5 $176.75   4.435%   $184.5889   $184.59   $184.60   $184.60  
  Purchase #6 $150.64   5.360%   $158.7143   $158.71   $158.70   $158.70  
  Purchase #7 $75.27   12.587%   $84.7442   $84.74   $84.75   $84.70  
  7 purchase totals = $1,108.04       $1,197.7846   $1,197.77   $1,197.80   $1,197.80