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 $202.27   11.556%   $225.6443   $225.64   $225.65   $225.60  
  Purchase #2 $155.89   13.321%   $176.6561   $176.66   $176.65   $176.70  
  Purchase #3 $117.37   13.767%   $133.5283   $133.53   $133.55   $133.50  
  Purchase #4 $151.29   13.279%   $171.3798   $171.38   $171.40   $171.40  
  Purchase #5 $194.44   4.356%   $202.9098   $202.91   $202.90   $202.90  
  Purchase #6 $33.38   10.540%   $36.8983   $36.90   $36.90   $36.90  
  Purchase #7 $136.69   6.726%   $145.8838   $145.88   $145.90   $145.90  
  7 purchase totals = $991.33       $1,092.9004   $1,092.90   $1,092.95   $1,092.90