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 $130.90   3.500%   $135.4815   $135.48   $135.50   $135.50  
  Purchase #2 $39.95   13.238%   $45.2386   $45.24   $45.25   $45.20  
  Purchase #3 $9.53   13.828%   $10.8478   $10.85   $10.85   $10.80  
  Purchase #4 $131.51   13.403%   $149.1363   $149.14   $149.15   $149.10  
  Purchase #5 $79.28   6.567%   $84.4863   $84.49   $84.50   $84.50  
  Purchase #6 $47.25   11.666%   $52.7622   $52.76   $52.75   $52.80  
  Purchase #7 $162.90   6.462%   $173.4266   $173.43   $173.45   $173.40  
  7 purchase totals = $601.32       $651.3793   $651.39   $651.45   $651.30