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 $222.38   4.321%   $231.989   $231.99   $232.00   $232.00  
  Purchase #2 $60.99   7.201%   $65.3819   $65.38   $65.40   $65.40  
  Purchase #3 $44.54   3.537%   $46.1154   $46.12   $46.10   $46.10  
  Purchase #4 $219.82   4.852%   $230.4857   $230.49   $230.50   $230.50  
  Purchase #5 $111.25   13.527%   $126.2988   $126.30   $126.30   $126.30  
  Purchase #6 $158.68   7.385%   $170.3985   $170.40   $170.40   $170.40  
  Purchase #7 $148.65   13.781%   $169.1355   $169.14   $169.15   $169.10  
  7 purchase totals = $966.31       $1,039.8048   $1,039.82   $1,039.85   $1,039.80