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 $249.53   12.662%   $281.1255   $281.13   $281.15   $281.10  
  Purchase #2 $46.45   9.206%   $50.7262   $50.73   $50.75   $50.70  
  Purchase #3 $17.61   8.476%   $19.1026   $19.10   $19.10   $19.10  
  Purchase #4 $198.38   6.407%   $211.0902   $211.09   $211.10   $211.10  
  Purchase #5 $176.97   12.413%   $198.9373   $198.94   $198.95   $198.90  
  Purchase #6 $249.26   5.843%   $263.8243   $263.82   $263.80   $263.80  
  Purchase #7 $72.33   6.391%   $76.9526   $76.95   $76.95   $77.00  
  7 purchase totals = $1,010.53       $1,101.7587   $1,101.76   $1,101.80   $1,101.70