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 $194.69   8.374%   $210.9933   $210.99   $211.00   $211.00  
  Purchase #2 $183.97   11.383%   $204.9113   $204.91   $204.90   $204.90  
  Purchase #3 $113.35   5.323%   $119.3836   $119.38   $119.40   $119.40  
  Purchase #4 $169.57   11.706%   $189.4199   $189.42   $189.40   $189.40  
  Purchase #5 $103.82   4.310%   $108.2946   $108.29   $108.30   $108.30  
  Purchase #6 $172.68   6.218%   $183.4172   $183.42   $183.40   $183.40  
  Purchase #7 $188.72   9.378%   $206.4182   $206.42   $206.40   $206.40  
  7 purchase totals = $1,126.80       $1,222.8381   $1,222.83   $1,222.80   $1,222.80