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 $202.89   13.656%   $230.5967   $230.60   $230.60   $230.60  
  Purchase #2 $98.60   12.735%   $111.1567   $111.16   $111.15   $111.20  
  Purchase #3 $93.40   8.742%   $101.565   $101.57   $101.55   $101.60  
  Purchase #4 $226.76   3.669%   $235.0798   $235.08   $235.10   $235.10  
  Purchase #5 $92.42   4.288%   $96.383   $96.38   $96.40   $96.40  
  Purchase #6 $24.26   10.725%   $26.8619   $26.86   $26.85   $26.90  
  Purchase #7 $157.37   9.493%   $172.3091   $172.31   $172.30   $172.30  
  7 purchase totals = $895.70       $973.9522   $973.96   $973.95   $974.10