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 $243.94   7.731%   $262.799   $262.80   $262.80   $262.80  
  Purchase #2 $173.76   8.793%   $189.0387   $189.04   $189.05   $189.00  
  Purchase #3 $57.96   8.254%   $62.744   $62.74   $62.75   $62.70  
  Purchase #4 $89.56   8.202%   $96.9057   $96.91   $96.90   $96.90  
  Purchase #5 $247.31   5.227%   $260.2369   $260.24   $260.25   $260.20  
  Purchase #6 $182.40   8.283%   $197.5082   $197.51   $197.50   $197.50  
  Purchase #7 $244.25   7.250%   $261.9581   $261.96   $261.95   $262.00  
  7 purchase totals = $1,239.18       $1,331.1906   $1,331.20   $1,331.20   $1,331.10