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 $115.49   12.596%   $130.0371   $130.04   $130.05   $130.00  
  Purchase #2 $66.92   13.641%   $76.0486   $76.05   $76.05   $76.00  
  Purchase #3 $250.58   6.664%   $267.2787   $267.28   $267.30   $267.30  
  Purchase #4 $96.54   5.125%   $101.4877   $101.49   $101.50   $101.50  
  Purchase #5 $205.39   13.274%   $232.6535   $232.65   $232.65   $232.70  
  Purchase #6 $211.96   13.251%   $240.0468   $240.05   $240.05   $240.00  
  Purchase #7 $12.88   5.607%   $13.6022   $13.60   $13.60   $13.60  
  7 purchase totals = $959.76       $1,061.1546   $1,061.16   $1,061.20   $1,061.10