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 $29.37   10.207%   $32.3678   $32.37   $32.35   $32.40  
  Purchase #2 $203.43   6.486%   $216.6245   $216.62   $216.60   $216.60  
  Purchase #3 $245.96   3.458%   $254.4653   $254.47   $254.45   $254.50  
  Purchase #4 $241.31   6.661%   $257.3837   $257.38   $257.40   $257.40  
  Purchase #5 $69.63   5.391%   $73.3838   $73.38   $73.40   $73.40  
  Purchase #6 $47.89   3.515%   $49.5733   $49.57   $49.55   $49.60  
  Purchase #7 $116.39   10.133%   $128.1838   $128.18   $128.20   $128.20  
  7 purchase totals = $953.98       $1,011.9822   $1,011.97   $1,011.95   $1,012.10