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 $90.44   6.282%   $96.1214   $96.12   $96.10   $96.10  
  Purchase #2 $121.76   7.388%   $130.7556   $130.76   $130.75   $130.80  
  Purchase #3 $147.69   9.626%   $161.9066   $161.91   $161.90   $161.90  
  Purchase #4 $245.92   7.267%   $263.791   $263.79   $263.80   $263.80  
  Purchase #5 $134.63   11.828%   $150.554   $150.55   $150.55   $150.60  
  Purchase #6 $209.35   6.296%   $222.5307   $222.53   $222.55   $222.50  
  Purchase #7 $245.43   6.511%   $261.4099   $261.41   $261.40   $261.40  
  7 purchase totals = $1,195.22       $1,287.0692   $1,287.07   $1,287.05   $1,287.10