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 $63.30   4.367%   $66.0643   $66.06   $66.05   $66.10  
  Purchase #2 $214.78   7.379%   $230.6286   $230.63   $230.65   $230.60  
  Purchase #3 $48.86   5.489%   $51.5419   $51.54   $51.55   $51.50  
  Purchase #4 $127.51   3.632%   $132.1412   $132.14   $132.15   $132.10  
  Purchase #5 $200.27   13.182%   $226.6696   $226.67   $226.65   $226.70  
  Purchase #6 $238.27   10.580%   $263.479   $263.48   $263.50   $263.50  
  Purchase #7 $192.68   13.347%   $218.397   $218.40   $218.40   $218.40  
  7 purchase totals = $1,085.67       $1,188.9216   $1,188.92   $1,188.95   $1,188.90