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 $233.72   6.305%   $248.456   $248.46   $248.45   $248.50  
  Purchase #2 $76.80   3.294%   $79.3298   $79.33   $79.35   $79.30  
  Purchase #3 $19.55   3.408%   $20.2163   $20.22   $20.20   $20.20  
  Purchase #4 $190.57   3.417%   $197.0818   $197.08   $197.10   $197.10  
  Purchase #5 $125.73   3.252%   $129.8187   $129.82   $129.80   $129.80  
  Purchase #6 $32.59   5.843%   $34.4942   $34.49   $34.50   $34.50  
  Purchase #7 $183.98   12.535%   $207.0419   $207.04   $207.05   $207.00  
  7 purchase totals = $862.94       $916.4387   $916.44   $916.45   $916.40