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 $249.41   7.451%   $267.9935   $267.99   $268.00   $268.00  
  Purchase #2 $108.26   11.740%   $120.9697   $120.97   $120.95   $121.00  
  Purchase #3 $5.27   6.485%   $5.6118   $5.61   $5.60   $5.60  
  Purchase #4 $42.68   5.556%   $45.0513   $45.05   $45.05   $45.10  
  Purchase #5 $50.37   6.115%   $53.4501   $53.45   $53.45   $53.50  
  Purchase #6 $247.72   11.392%   $275.9403   $275.94   $275.95   $275.90  
  Purchase #7 $168.88   9.729%   $185.3103   $185.31   $185.30   $185.30  
  7 purchase totals = $872.59       $954.3270   $954.32   $954.30   $954.40