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 $121.53   4.108%   $126.5225   $126.52   $126.50   $126.50  
  Purchase #2 $150.63   13.253%   $170.593   $170.59   $170.60   $170.60  
  Purchase #3 $102.73   13.117%   $116.2051   $116.21   $116.20   $116.20  
  Purchase #4 $228.38   5.562%   $241.0825   $241.08   $241.10   $241.10  
  Purchase #5 $32.36   13.228%   $36.6406   $36.64   $36.65   $36.60  
  Purchase #6 $207.37   9.602%   $227.2817   $227.28   $227.30   $227.30  
  Purchase #7 $213.48   6.157%   $226.624   $226.62   $226.60   $226.60  
  7 purchase totals = $1,056.48       $1,144.9494   $1,144.94   $1,144.95   $1,144.90