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 $131.85   7.420%   $141.6333   $141.63   $141.65   $141.60  
  Purchase #2 $80.38   7.214%   $86.1786   $86.18   $86.20   $86.20  
  Purchase #3 $150.82   3.827%   $156.5919   $156.59   $156.60   $156.60  
  Purchase #4 $85.66   3.278%   $88.4679   $88.47   $88.45   $88.50  
  Purchase #5 $183.48   7.485%   $197.2135   $197.21   $197.20   $197.20  
  Purchase #6 $85.98   7.632%   $92.542   $92.54   $92.55   $92.50  
  Purchase #7 $236.46   10.357%   $260.9502   $260.95   $260.95   $261.00  
  7 purchase totals = $954.63       $1,023.5774   $1,023.57   $1,023.60   $1,023.60