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 $181.83   7.207%   $194.9345   $194.93   $194.95   $194.90  
  Purchase #2 $240.62   5.437%   $253.7025   $253.70   $253.70   $253.70  
  Purchase #3 $140.95   8.342%   $152.708   $152.71   $152.70   $152.70  
  Purchase #4 $104.53   8.851%   $113.782   $113.78   $113.80   $113.80  
  Purchase #5 $135.55   12.123%   $151.9827   $151.98   $152.00   $152.00  
  Purchase #6 $168.56   10.594%   $186.4172   $186.42   $186.40   $186.40  
  Purchase #7 $13.98   7.160%   $14.981   $14.98   $15.00   $15.00  
  7 purchase totals = $986.02       $1,068.5079   $1,068.50   $1,068.55   $1,068.50