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 $22.77   12.636%   $25.6472   $25.65   $25.65   $25.60  
  Purchase #2 $219.76   6.471%   $233.9807   $233.98   $234.00   $234.00  
  Purchase #3 $45.51   8.338%   $49.3046   $49.30   $49.30   $49.30  
  Purchase #4 $232.95   11.694%   $260.1912   $260.19   $260.20   $260.20  
  Purchase #5 $206.67   4.328%   $215.6147   $215.61   $215.60   $215.60  
  Purchase #6 $25.32   10.520%   $27.9837   $27.98   $28.00   $28.00  
  Purchase #7 $238.60   5.464%   $251.6371   $251.64   $251.65   $251.60  
  7 purchase totals = $991.58       $1,064.3592   $1,064.35   $1,064.40   $1,064.30