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 $171.57   6.779%   $183.2007   $183.20   $183.20   $183.20  
  Purchase #2 $172.55   13.458%   $195.7718   $195.77   $195.75   $195.80  
  Purchase #3 $170.69   10.134%   $187.9877   $187.99   $188.00   $188.00  
  Purchase #4 $157.60   7.485%   $169.3964   $169.40   $169.40   $169.40  
  Purchase #5 $61.59   6.146%   $65.3753   $65.38   $65.40   $65.40  
  Purchase #6 $23.59   11.224%   $26.2377   $26.24   $26.25   $26.20  
  Purchase #7 $167.40   3.204%   $172.7635   $172.76   $172.75   $172.80  
  7 purchase totals = $924.99       $1,000.7331   $1,000.74   $1,000.75   $1,000.80