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 $9.28   6.189%   $9.8543   $9.85   $9.85   $9.90  
  Purchase #2 $236.40   3.349%   $244.317   $244.32   $244.30   $244.30  
  Purchase #3 $171.95   10.274%   $189.6161   $189.62   $189.60   $189.60  
  Purchase #4 $221.48   13.125%   $250.5493   $250.55   $250.55   $250.50  
  Purchase #5 $34.83   10.190%   $38.3792   $38.38   $38.40   $38.40  
  Purchase #6 $14.82   13.707%   $16.8514   $16.85   $16.85   $16.90  
  Purchase #7 $243.96   4.732%   $255.5042   $255.50   $255.50   $255.50  
  7 purchase totals = $932.72       $1,005.0715   $1,005.07   $1,005.05   $1,005.10