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 $68.81   7.761%   $74.1503   $74.15   $74.15   $74.20  
  Purchase #2 $174.62   11.676%   $195.0086   $195.01   $195.00   $195.00  
  Purchase #3 $44.63   7.321%   $47.8974   $47.90   $47.90   $47.90  
  Purchase #4 $212.91   7.262%   $228.3715   $228.37   $228.35   $228.40  
  Purchase #5 $190.52   3.650%   $197.474   $197.47   $197.45   $197.50  
  Purchase #6 $57.62   4.762%   $60.3639   $60.36   $60.35   $60.40  
  Purchase #7 $32.97   9.641%   $36.1486   $36.15   $36.15   $36.10  
  7 purchase totals = $782.08       $839.4143   $839.41   $839.35   $839.50