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 $53.49   12.204%   $60.0179   $60.02   $60.00   $60.00  
  Purchase #2 $99.96   10.586%   $110.5418   $110.54   $110.55   $110.50  
  Purchase #3 $232.73   6.228%   $247.2244   $247.22   $247.20   $247.20  
  Purchase #4 $158.36   8.300%   $171.5039   $171.50   $171.50   $171.50  
  Purchase #5 $61.48   11.264%   $68.4051   $68.41   $68.40   $68.40  
  Purchase #6 $32.61   4.838%   $34.1877   $34.19   $34.20   $34.20  
  Purchase #7 $26.80   7.681%   $28.8585   $28.86   $28.85   $28.90  
  7 purchase totals = $665.43       $720.7393   $720.74   $720.70   $720.70