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 $62.53   7.357%   $67.1303   $67.13   $67.15   $67.10  
  Purchase #2 $198.95   8.864%   $216.5849   $216.58   $216.60   $216.60  
  Purchase #3 $178.75   10.419%   $197.374   $197.37   $197.35   $197.40  
  Purchase #4 $57.71   12.770%   $65.0796   $65.08   $65.10   $65.10  
  Purchase #5 $111.92   10.802%   $124.0096   $124.01   $124.00   $124.00  
  Purchase #6 $92.39   12.659%   $104.0857   $104.09   $104.10   $104.10  
  Purchase #7 $47.27   5.663%   $49.9469   $49.95   $49.95   $49.90  
  7 purchase totals = $749.52       $824.2110   $824.21   $824.25   $824.20