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 $220.55   11.653%   $246.2507   $246.25   $246.25   $246.30  
  Purchase #2 $169.71   4.832%   $177.9104   $177.91   $177.90   $177.90  
  Purchase #3 $175.89   3.777%   $182.5334   $182.53   $182.55   $182.50  
  Purchase #4 $233.37   13.599%   $265.106   $265.11   $265.10   $265.10  
  Purchase #5 $197.34   9.121%   $215.3394   $215.34   $215.35   $215.30  
  Purchase #6 $79.30   5.377%   $83.564   $83.56   $83.55   $83.60  
  Purchase #7 $200.54   7.598%   $215.777   $215.78   $215.80   $215.80  
  7 purchase totals = $1,276.70       $1,386.4809   $1,386.48   $1,386.50   $1,386.50