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 $84.82   8.846%   $92.3232   $92.32   $92.30   $92.30  
  Purchase #2 $88.49   4.303%   $92.2977   $92.30   $92.30   $92.30  
  Purchase #3 $245.82   12.509%   $276.5696   $276.57   $276.55   $276.60  
  Purchase #4 $83.82   10.451%   $92.58   $92.58   $92.60   $92.60  
  Purchase #5 $170.51   8.389%   $184.8141   $184.81   $184.80   $184.80  
  Purchase #6 $43.89   13.282%   $49.7195   $49.72   $49.70   $49.70  
  Purchase #7 $162.51   8.602%   $176.4891   $176.49   $176.50   $176.50  
  7 purchase totals = $879.86       $964.7932   $964.79   $964.75   $964.80