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 $86.84   5.113%   $91.2801   $91.28   $91.30   $91.30  
  Purchase #2 $132.93   9.792%   $145.9465   $145.95   $145.95   $145.90  
  Purchase #3 $39.68   11.557%   $44.2658   $44.27   $44.25   $44.30  
  Purchase #4 $241.93   11.354%   $269.3987   $269.40   $269.40   $269.40  
  Purchase #5 $54.66   4.821%   $57.2952   $57.30   $57.30   $57.30  
  Purchase #6 $65.65   3.106%   $67.6891   $67.69   $67.70   $67.70  
  Purchase #7 $148.54   5.751%   $157.0825   $157.08   $157.10   $157.10  
  7 purchase totals = $770.23       $832.9579   $832.97   $833.00   $833.00