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 $88.63   6.686%   $94.5558   $94.56   $94.55   $94.60  
  Purchase #2 $56.58   3.277%   $58.4341   $58.43   $58.45   $58.40  
  Purchase #3 $63.58   4.862%   $66.6713   $66.67   $66.65   $66.70  
  Purchase #4 $232.34   10.283%   $256.2315   $256.23   $256.25   $256.20  
  Purchase #5 $112.94   11.726%   $126.1833   $126.18   $126.20   $126.20  
  Purchase #6 $126.28   13.367%   $143.1598   $143.16   $143.15   $143.20  
  Purchase #7 $163.94   9.182%   $178.993   $178.99   $179.00   $179.00  
  7 purchase totals = $844.29       $924.2288   $924.22   $924.25   $924.30