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 $54.74   10.167%   $60.3054   $60.31   $60.30   $60.30  
  Purchase #2 $205.79   5.291%   $216.6783   $216.68   $216.70   $216.70  
  Purchase #3 $62.71   11.350%   $69.8276   $69.83   $69.85   $69.80  
  Purchase #4 $129.94   8.791%   $141.363   $141.36   $141.35   $141.40  
  Purchase #5 $213.69   8.766%   $232.4221   $232.42   $232.40   $232.40  
  Purchase #6 $115.88   11.403%   $129.0938   $129.09   $129.10   $129.10  
  Purchase #7 $225.26   11.409%   $250.9599   $250.96   $250.95   $251.00  
  7 purchase totals = $1,008.01       $1,100.6501   $1,100.65   $1,100.65   $1,100.70