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 $64.97   12.760%   $73.2602   $73.26   $73.25   $73.30  
  Purchase #2 $158.65   13.190%   $179.5759   $179.58   $179.60   $179.60  
  Purchase #3 $89.46   4.743%   $93.7031   $93.70   $93.70   $93.70  
  Purchase #4 $138.86   9.825%   $152.503   $152.50   $152.50   $152.50  
  Purchase #5 $129.77   13.114%   $146.788   $146.79   $146.80   $146.80  
  Purchase #6 $161.67   11.171%   $179.7302   $179.73   $179.75   $179.70  
  Purchase #7 $112.41   5.663%   $118.7758   $118.78   $118.80   $118.80  
  7 purchase totals = $855.79       $944.3362   $944.34   $944.40   $944.40