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 $84.59   13.139%   $95.7043   $95.70   $95.70   $95.70  
  Purchase #2 $123.98   8.443%   $134.4476   $134.45   $134.45   $134.40  
  Purchase #3 $103.80   11.332%   $115.5626   $115.56   $115.55   $115.60  
  Purchase #4 $80.71   6.451%   $85.9166   $85.92   $85.90   $85.90  
  Purchase #5 $132.75   3.365%   $137.217   $137.22   $137.20   $137.20  
  Purchase #6 $199.47   8.779%   $216.9815   $216.98   $217.00   $217.00  
  Purchase #7 $46.53   6.247%   $49.4367   $49.44   $49.45   $49.40  
  7 purchase totals = $771.83       $835.2663   $835.27   $835.25   $835.20