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 $155.68   12.506%   $175.1493   $175.15   $175.15   $175.10  
  Purchase #2 $241.73   11.259%   $268.9464   $268.95   $268.95   $268.90  
  Purchase #3 $244.88   5.158%   $257.5109   $257.51   $257.50   $257.50  
  Purchase #4 $138.92   5.803%   $146.9815   $146.98   $147.00   $147.00  
  Purchase #5 $237.82   6.644%   $253.6208   $253.62   $253.60   $253.60  
  Purchase #6 $243.40   9.226%   $265.8561   $265.86   $265.85   $265.90  
  Purchase #7 $89.43   13.643%   $101.6309   $101.63   $101.65   $101.60  
  7 purchase totals = $1,351.86       $1,469.6959   $1,469.70   $1,469.70   $1,469.60