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 $54.44   9.743%   $59.7441   $59.74   $59.75   $59.70  
  Purchase #2 $219.40   10.416%   $242.2527   $242.25   $242.25   $242.30  
  Purchase #3 $171.28   3.361%   $177.0367   $177.04   $177.05   $177.00  
  Purchase #4 $64.33   5.599%   $67.9318   $67.93   $67.95   $67.90  
  Purchase #5 $193.53   8.222%   $209.442   $209.44   $209.45   $209.40  
  Purchase #6 $207.25   12.226%   $232.5884   $232.59   $232.60   $232.60  
  Purchase #7 $86.42   12.331%   $97.0765   $97.08   $97.10   $97.10  
  7 purchase totals = $996.65       $1,086.0722   $1,086.07   $1,086.15   $1,086.00