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 $186.29   13.553%   $211.5379   $211.54   $211.55   $211.50  
  Purchase #2 $81.59   13.603%   $92.6887   $92.69   $92.70   $92.70  
  Purchase #3 $221.63   9.140%   $241.887   $241.89   $241.90   $241.90  
  Purchase #4 $231.46   8.820%   $251.8748   $251.87   $251.85   $251.90  
  Purchase #5 $53.86   6.734%   $57.4869   $57.49   $57.50   $57.50  
  Purchase #6 $109.34   5.415%   $115.2608   $115.26   $115.25   $115.30  
  Purchase #7 $223.99   4.535%   $234.1479   $234.15   $234.15   $234.10  
  7 purchase totals = $1,108.16       $1,204.8840   $1,204.89   $1,204.90   $1,204.90