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 $90.60   3.271%   $93.5635   $93.56   $93.55   $93.60  
  Purchase #2 $219.94   4.531%   $229.9055   $229.91   $229.90   $229.90  
  Purchase #3 $18.86   9.629%   $20.676   $20.68   $20.70   $20.70  
  Purchase #4 $27.75   7.144%   $29.7325   $29.73   $29.75   $29.70  
  Purchase #5 $245.97   7.178%   $263.6257   $263.63   $263.65   $263.60  
  Purchase #6 $245.51   13.790%   $279.3658   $279.37   $279.35   $279.40  
  Purchase #7 $139.29   3.166%   $143.6999   $143.70   $143.70   $143.70  
  7 purchase totals = $987.92       $1,060.5689   $1,060.58   $1,060.60   $1,060.60