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 $88.64   11.607%   $98.9284   $98.93   $98.95   $98.90  
  Purchase #2 $173.97   5.647%   $183.7941   $183.79   $183.80   $183.80  
  Purchase #3 $211.97   13.438%   $240.4545   $240.45   $240.45   $240.50  
  Purchase #4 $136.28   11.302%   $151.6824   $151.68   $151.70   $151.70  
  Purchase #5 $87.74   8.559%   $95.2497   $95.25   $95.25   $95.20  
  Purchase #6 $129.98   11.708%   $145.1981   $145.20   $145.20   $145.20  
  Purchase #7 $188.56   13.433%   $213.8893   $213.89   $213.90   $213.90  
  7 purchase totals = $1,017.14       $1,129.1965   $1,129.19   $1,129.25   $1,129.20