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 $246.53   12.459%   $277.2452   $277.25   $277.25   $277.20  
  Purchase #2 $214.35   5.267%   $225.6398   $225.64   $225.65   $225.60  
  Purchase #3 $48.66   13.263%   $55.1138   $55.11   $55.10   $55.10  
  Purchase #4 $206.88   12.217%   $232.1545   $232.15   $232.15   $232.20  
  Purchase #5 $20.40   10.518%   $22.5457   $22.55   $22.55   $22.50  
  Purchase #6 $22.26   3.421%   $23.0215   $23.02   $23.00   $23.00  
  Purchase #7 $162.99   13.742%   $185.3881   $185.39   $185.40   $185.40  
  7 purchase totals = $922.07       $1,021.1086   $1,021.11   $1,021.10   $1,021.00