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 $86.95   10.684%   $96.2397   $96.24   $96.25   $96.20  
  Purchase #2 $120.91   8.473%   $131.1547   $131.15   $131.15   $131.20  
  Purchase #3 $136.65   4.119%   $142.2786   $142.28   $142.30   $142.30  
  Purchase #4 $180.87   12.798%   $204.0177   $204.02   $204.00   $204.00  
  Purchase #5 $220.29   12.771%   $248.4232   $248.42   $248.40   $248.40  
  Purchase #6 $217.37   10.580%   $240.3677   $240.37   $240.35   $240.40  
  Purchase #7 $10.30   10.164%   $11.3469   $11.35   $11.35   $11.30  
  7 purchase totals = $973.34       $1,073.8285   $1,073.83   $1,073.80   $1,073.80