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 $95.80   8.654%   $104.0905   $104.09   $104.10   $104.10  
  Purchase #2 $88.72   9.143%   $96.8317   $96.83   $96.85   $96.80  
  Purchase #3 $161.68   4.490%   $168.9394   $168.94   $168.95   $168.90  
  Purchase #4 $54.34   6.847%   $58.0607   $58.06   $58.05   $58.10  
  Purchase #5 $14.41   7.480%   $15.4879   $15.49   $15.50   $15.50  
  Purchase #6 $117.95   3.786%   $122.4156   $122.42   $122.40   $122.40  
  Purchase #7 $37.25   4.372%   $38.8786   $38.88   $38.90   $38.90  
  7 purchase totals = $570.15       $604.7044   $604.71   $604.75   $604.70