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 $41.32   12.744%   $46.5858   $46.59   $46.60   $46.60  
  Purchase #2 $231.43   4.256%   $241.2797   $241.28   $241.30   $241.30  
  Purchase #3 $223.67   13.781%   $254.494   $254.49   $254.50   $254.50  
  Purchase #4 $101.46   12.720%   $114.3657   $114.37   $114.35   $114.40  
  Purchase #5 $136.59   10.612%   $151.0849   $151.08   $151.10   $151.10  
  Purchase #6 $10.86   6.583%   $11.5749   $11.57   $11.55   $11.60  
  Purchase #7 $141.29   11.501%   $157.5398   $157.54   $157.55   $157.50  
  7 purchase totals = $886.62       $976.9248   $976.92   $976.95   $977.00