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 $86.32   11.821%   $96.5239   $96.52   $96.50   $96.50  
  Purchase #2 $205.28   9.766%   $225.3276   $225.33   $225.35   $225.30  
  Purchase #3 $74.42   8.595%   $80.8164   $80.82   $80.80   $80.80  
  Purchase #4 $115.41   8.628%   $125.3676   $125.37   $125.35   $125.40  
  Purchase #5 $250.47   5.796%   $264.9872   $264.99   $265.00   $265.00  
  Purchase #6 $236.53   8.149%   $255.8048   $255.80   $255.80   $255.80  
  Purchase #7 $220.48   12.543%   $248.1348   $248.13   $248.15   $248.10  
  7 purchase totals = $1,188.91       $1,296.9623   $1,296.96   $1,296.95   $1,296.90