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 $227.77   12.368%   $255.9406   $255.94   $255.95   $255.90  
  Purchase #2 $241.85   4.749%   $253.3355   $253.34   $253.35   $253.30  
  Purchase #3 $201.31   7.645%   $216.7001   $216.70   $216.70   $216.70  
  Purchase #4 $125.68   5.482%   $132.5698   $132.57   $132.55   $132.60  
  Purchase #5 $222.86   13.678%   $253.3428   $253.34   $253.35   $253.30  
  Purchase #6 $100.61   7.519%   $108.1749   $108.17   $108.15   $108.20  
  Purchase #7 $40.93   6.510%   $43.5945   $43.59   $43.60   $43.60  
  7 purchase totals = $1,161.01       $1,263.6582   $1,263.65   $1,263.65   $1,263.60