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 $84.67   10.211%   $93.3157   $93.32   $93.30   $93.30  
  Purchase #2 $25.59   8.335%   $27.7229   $27.72   $27.70   $27.70  
  Purchase #3 $226.87   13.817%   $258.2166   $258.22   $258.20   $258.20  
  Purchase #4 $70.67   7.174%   $75.7399   $75.74   $75.75   $75.70  
  Purchase #5 $206.41   7.394%   $221.672   $221.67   $221.65   $221.70  
  Purchase #6 $96.79   12.446%   $108.8365   $108.84   $108.85   $108.80  
  Purchase #7 $225.90   5.548%   $238.4329   $238.43   $238.45   $238.40  
  7 purchase totals = $936.90       $1,023.9365   $1,023.94   $1,023.90   $1,023.80