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 $183.85   11.776%   $205.5002   $205.50   $205.50   $205.50  
  Purchase #2 $250.81   6.199%   $266.3577   $266.36   $266.35   $266.40  
  Purchase #3 $100.99   3.603%   $104.6287   $104.63   $104.65   $104.60  
  Purchase #4 $16.79   5.795%   $17.763   $17.76   $17.75   $17.80  
  Purchase #5 $86.50   12.166%   $97.0236   $97.02   $97.00   $97.00  
  Purchase #6 $69.90   6.180%   $74.2198   $74.22   $74.20   $74.20  
  Purchase #7 $87.75   13.490%   $99.5875   $99.59   $99.60   $99.60  
  7 purchase totals = $796.59       $865.0805   $865.08   $865.05   $865.10