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 $51.73   11.198%   $57.5227   $57.52   $57.50   $57.50  
  Purchase #2 $103.64   10.505%   $114.5274   $114.53   $114.55   $114.50  
  Purchase #3 $88.88   7.314%   $95.3807   $95.38   $95.40   $95.40  
  Purchase #4 $206.89   9.306%   $226.1432   $226.14   $226.15   $226.10  
  Purchase #5 $192.45   5.650%   $203.3234   $203.32   $203.30   $203.30  
  Purchase #6 $238.28   11.246%   $265.077   $265.08   $265.10   $265.10  
  Purchase #7 $119.39   5.764%   $126.2716   $126.27   $126.25   $126.30  
  7 purchase totals = $1,001.26       $1,088.2460   $1,088.24   $1,088.25   $1,088.20