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 $66.89   10.789%   $74.1068   $74.11   $74.10   $74.10  
  Purchase #2 $54.64   11.639%   $60.9995   $61.00   $61.00   $61.00  
  Purchase #3 $100.62   3.471%   $104.1125   $104.11   $104.10   $104.10  
  Purchase #4 $179.94   8.203%   $194.7005   $194.70   $194.70   $194.70  
  Purchase #5 $32.25   3.809%   $33.4784   $33.48   $33.50   $33.50  
  Purchase #6 $213.81   10.383%   $236.0099   $236.01   $236.00   $236.00  
  Purchase #7 $47.87   3.546%   $49.5675   $49.57   $49.55   $49.60  
  7 purchase totals = $696.02       $752.9751   $752.98   $752.95   $753.00