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 $89.88   6.581%   $95.795   $95.80   $95.80   $95.80  
  Purchase #2 $120.40   12.651%   $135.6318   $135.63   $135.65   $135.60  
  Purchase #3 $239.51   11.293%   $266.5579   $266.56   $266.55   $266.60  
  Purchase #4 $155.80   8.555%   $169.1287   $169.13   $169.15   $169.10  
  Purchase #5 $206.26   7.169%   $221.0468   $221.05   $221.05   $221.00  
  Purchase #6 $45.79   5.435%   $48.2787   $48.28   $48.30   $48.30  
  Purchase #7 $45.68   8.135%   $49.3961   $49.40   $49.40   $49.40  
  7 purchase totals = $903.32       $985.8350   $985.85   $985.90   $985.80