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 $216.96   7.202%   $232.5855   $232.59   $232.60   $232.60  
  Purchase #2 $72.25   6.427%   $76.8935   $76.89   $76.90   $76.90  
  Purchase #3 $221.35   6.635%   $236.0366   $236.04   $236.05   $236.00  
  Purchase #4 $78.29   8.292%   $84.7818   $84.78   $84.80   $84.80  
  Purchase #5 $68.65   12.746%   $77.4001   $77.40   $77.40   $77.40  
  Purchase #6 $113.72   4.653%   $119.0114   $119.01   $119.00   $119.00  
  Purchase #7 $128.41   5.523%   $135.5021   $135.50   $135.50   $135.50  
  7 purchase totals = $899.63       $962.2110   $962.21   $962.25   $962.20