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 $169.92   8.369%   $184.1406   $184.14   $184.15   $184.10  
  Purchase #2 $214.47   8.635%   $232.9895   $232.99   $233.00   $233.00  
  Purchase #3 $237.56   12.806%   $267.9819   $267.98   $268.00   $268.00  
  Purchase #4 $6.48   12.462%   $7.2875   $7.29   $7.30   $7.30  
  Purchase #5 $227.92   5.741%   $241.0049   $241.00   $241.00   $241.00  
  Purchase #6 $22.45   11.792%   $25.0973   $25.10   $25.10   $25.10  
  Purchase #7 $60.97   5.427%   $64.2788   $64.28   $64.30   $64.30  
  7 purchase totals = $939.77       $1,022.7805   $1,022.78   $1,022.85   $1,022.80