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 $246.68   5.536%   $260.3362   $260.34   $260.35   $260.30  
  Purchase #2 $216.44   9.204%   $236.3611   $236.36   $236.35   $236.40  
  Purchase #3 $50.31   7.441%   $54.0536   $54.05   $54.05   $54.10  
  Purchase #4 $62.67   9.499%   $68.623   $68.62   $68.60   $68.60  
  Purchase #5 $124.94   5.348%   $131.6218   $131.62   $131.60   $131.60  
  Purchase #6 $209.75   11.170%   $233.1791   $233.18   $233.20   $233.20  
  Purchase #7 $201.57   9.858%   $221.4408   $221.44   $221.45   $221.40  
  7 purchase totals = $1,112.36       $1,205.6156   $1,205.61   $1,205.60   $1,205.60