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 $188.29   5.552%   $198.7439   $198.74   $198.75   $198.70  
  Purchase #2 $31.29   10.306%   $34.5147   $34.51   $34.50   $34.50  
  Purchase #3 $237.44   5.156%   $249.6824   $249.68   $249.70   $249.70  
  Purchase #4 $84.56   5.156%   $88.9199   $88.92   $88.90   $88.90  
  Purchase #5 $233.99   6.599%   $249.431   $249.43   $249.45   $249.40  
  Purchase #6 $161.75   7.762%   $174.305   $174.31   $174.30   $174.30  
  Purchase #7 $37.38   7.754%   $40.2784   $40.28   $40.30   $40.30  
  7 purchase totals = $974.70       $1,035.8753   $1,035.87   $1,035.90   $1,035.80