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 $224.44   9.576%   $245.9324   $245.93   $245.95   $245.90  
  Purchase #2 $111.60   6.277%   $118.6051   $118.61   $118.60   $118.60  
  Purchase #3 $115.29   5.215%   $121.3024   $121.30   $121.30   $121.30  
  Purchase #4 $187.79   5.673%   $198.4433   $198.44   $198.45   $198.40  
  Purchase #5 $166.25   9.648%   $182.2898   $182.29   $182.30   $182.30  
  Purchase #6 $49.29   10.556%   $54.4931   $54.49   $54.50   $54.50  
  Purchase #7 $177.94   8.373%   $192.8389   $192.84   $192.85   $192.80  
  7 purchase totals = $1,032.60       $1,113.9050   $1,113.90   $1,113.95   $1,113.80