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 $83.69   10.698%   $92.6432   $92.64   $92.65   $92.60  
  Purchase #2 $53.53   3.344%   $55.32   $55.32   $55.30   $55.30  
  Purchase #3 $43.35   6.545%   $46.1873   $46.19   $46.20   $46.20  
  Purchase #4 $159.27   10.165%   $175.4598   $175.46   $175.45   $175.50  
  Purchase #5 $18.57   9.292%   $20.2955   $20.30   $20.30   $20.30  
  Purchase #6 $242.34   8.849%   $263.7847   $263.78   $263.80   $263.80  
  Purchase #7 $166.45   7.580%   $179.0669   $179.07   $179.05   $179.10  
  7 purchase totals = $767.20       $832.7574   $832.76   $832.75   $832.80