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 $54.28   6.692%   $57.9124   $57.91   $57.90   $57.90  
  Purchase #2 $169.43   12.283%   $190.2411   $190.24   $190.25   $190.20  
  Purchase #3 $196.46   3.266%   $202.8764   $202.88   $202.90   $202.90  
  Purchase #4 $71.76   5.364%   $75.6092   $75.61   $75.60   $75.60  
  Purchase #5 $248.81   9.201%   $271.703   $271.70   $271.70   $271.70  
  Purchase #6 $249.47   7.499%   $268.1778   $268.18   $268.20   $268.20  
  Purchase #7 $183.92   9.370%   $201.1533   $201.15   $201.15   $201.20  
  7 purchase totals = $1,174.13       $1,267.6732   $1,267.67   $1,267.70   $1,267.70