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 $223.70   13.476%   $253.8458   $253.85   $253.85   $253.80  
  Purchase #2 $127.63   4.468%   $133.3325   $133.33   $133.35   $133.30  
  Purchase #3 $135.64   12.578%   $152.7008   $152.70   $152.70   $152.70  
  Purchase #4 $166.92   5.208%   $175.6132   $175.61   $175.60   $175.60  
  Purchase #5 $25.34   4.345%   $26.441   $26.44   $26.45   $26.40  
  Purchase #6 $191.70   4.173%   $199.6996   $199.70   $199.70   $199.70  
  Purchase #7 $72.30   10.224%   $79.692   $79.69   $79.70   $79.70  
  7 purchase totals = $943.23       $1,021.3249   $1,021.32   $1,021.35   $1,021.20