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 $57.71   11.570%   $64.387   $64.39   $64.40   $64.40  
  Purchase #2 $7.79   9.132%   $8.5014   $8.50   $8.50   $8.50  
  Purchase #3 $160.47   5.625%   $169.4964   $169.50   $169.50   $169.50  
  Purchase #4 $22.83   13.328%   $25.8728   $25.87   $25.85   $25.90  
  Purchase #5 $241.34   4.800%   $252.9243   $252.92   $252.90   $252.90  
  Purchase #6 $31.42   8.188%   $33.9927   $33.99   $34.00   $34.00  
  Purchase #7 $170.25   4.180%   $177.3665   $177.37   $177.35   $177.40  
  7 purchase totals = $691.81       $732.5411   $732.54   $732.50   $732.60