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 $81.58   12.831%   $92.0475   $92.05   $92.05   $92.00  
  Purchase #2 $83.41   13.373%   $94.5644   $94.56   $94.55   $94.60  
  Purchase #3 $110.61   5.569%   $116.7699   $116.77   $116.75   $116.80  
  Purchase #4 $246.27   12.481%   $277.007   $277.01   $277.00   $277.00  
  Purchase #5 $199.36   8.836%   $216.9754   $216.98   $217.00   $217.00  
  Purchase #6 $32.57   11.448%   $36.2986   $36.30   $36.30   $36.30  
  Purchase #7 $121.48   6.867%   $129.822   $129.82   $129.80   $129.80  
  7 purchase totals = $875.28       $963.4848   $963.49   $963.45   $963.50