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 $45.28   9.763%   $49.7007   $49.70   $49.70   $49.70  
  Purchase #2 $217.41   10.374%   $239.9641   $239.96   $239.95   $240.00  
  Purchase #3 $202.32   3.663%   $209.731   $209.73   $209.75   $209.70  
  Purchase #4 $219.73   10.151%   $242.0348   $242.03   $242.05   $242.00  
  Purchase #5 $139.67   10.136%   $153.827   $153.83   $153.85   $153.80  
  Purchase #6 $210.88   3.273%   $217.7821   $217.78   $217.80   $217.80  
  Purchase #7 $179.43   5.690%   $189.6396   $189.64   $189.65   $189.60  
  7 purchase totals = $1,214.72       $1,302.6793   $1,302.67   $1,302.75   $1,302.60