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 $57.68   12.137%   $64.6806   $64.68   $64.70   $64.70  
  Purchase #2 $156.63   6.543%   $166.8783   $166.88   $166.90   $166.90  
  Purchase #3 $38.28   8.773%   $41.6383   $41.64   $41.65   $41.60  
  Purchase #4 $244.80   4.369%   $255.4953   $255.50   $255.50   $255.50  
  Purchase #5 $114.56   13.159%   $129.635   $129.64   $129.65   $129.60  
  Purchase #6 $138.35   6.227%   $146.9651   $146.97   $146.95   $147.00  
  Purchase #7 $136.48   4.599%   $142.7567   $142.76   $142.75   $142.80  
  7 purchase totals = $886.78       $948.0493   $948.07   $948.10   $948.10