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 $134.67   8.634%   $146.2974   $146.30   $146.30   $146.30  
  Purchase #2 $247.25   6.358%   $262.9702   $262.97   $262.95   $263.00  
  Purchase #3 $205.55   4.796%   $215.4082   $215.41   $215.40   $215.40  
  Purchase #4 $200.95   6.271%   $213.5516   $213.55   $213.55   $213.60  
  Purchase #5 $171.93   4.150%   $179.0651   $179.07   $179.05   $179.10  
  Purchase #6 $55.86   11.358%   $62.2046   $62.20   $62.20   $62.20  
  Purchase #7 $90.34   3.134%   $93.1713   $93.17   $93.15   $93.20  
  7 purchase totals = $1,106.55       $1,172.6684   $1,172.67   $1,172.60   $1,172.80