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 $245.75   6.654%   $262.1022   $262.10   $262.10   $262.10  
  Purchase #2 $70.97   5.559%   $74.9152   $74.92   $74.90   $74.90  
  Purchase #3 $250.50   4.359%   $261.4193   $261.42   $261.40   $261.40  
  Purchase #4 $82.96   6.704%   $88.5216   $88.52   $88.50   $88.50  
  Purchase #5 $129.50   7.454%   $139.1529   $139.15   $139.15   $139.20  
  Purchase #6 $34.60   6.739%   $36.9317   $36.93   $36.95   $36.90  
  Purchase #7 $170.94   12.685%   $192.6237   $192.62   $192.60   $192.60  
  7 purchase totals = $985.22       $1,055.6666   $1,055.66   $1,055.60   $1,055.60