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 $57.84   6.802%   $61.7743   $61.77   $61.75   $61.80  
  Purchase #2 $235.51   11.871%   $263.4674   $263.47   $263.45   $263.50  
  Purchase #3 $121.89   6.293%   $129.5605   $129.56   $129.55   $129.60  
  Purchase #4 $87.57   12.746%   $98.7317   $98.73   $98.75   $98.70  
  Purchase #5 $9.96   9.347%   $10.891   $10.89   $10.90   $10.90  
  Purchase #6 $105.88   4.574%   $110.723   $110.72   $110.70   $110.70  
  Purchase #7 $112.63   13.584%   $127.9297   $127.93   $127.95   $127.90  
  7 purchase totals = $731.28       $803.0776   $803.07   $803.05   $803.10