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 $88.57   6.292%   $94.1428   $94.14   $94.15   $94.10  
  Purchase #2 $155.41   8.558%   $168.71   $168.71   $168.70   $168.70  
  Purchase #3 $98.26   5.865%   $104.0229   $104.02   $104.00   $104.00  
  Purchase #4 $221.39   12.825%   $249.7833   $249.78   $249.80   $249.80  
  Purchase #5 $67.67   9.717%   $74.2455   $74.25   $74.25   $74.20  
  Purchase #6 $173.76   6.263%   $184.6426   $184.64   $184.65   $184.60  
  Purchase #7 $113.74   5.168%   $119.6181   $119.62   $119.60   $119.60  
  7 purchase totals = $918.80       $995.1652   $995.16   $995.15   $995.00