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 $59.77   11.245%   $66.4911   $66.49   $66.50   $66.50  
  Purchase #2 $239.72   3.861%   $248.9756   $248.98   $249.00   $249.00  
  Purchase #3 $116.36   4.404%   $121.4845   $121.48   $121.50   $121.50  
  Purchase #4 $187.38   9.672%   $205.5034   $205.50   $205.50   $205.50  
  Purchase #5 $62.32   8.405%   $67.558   $67.56   $67.55   $67.60  
  Purchase #6 $211.41   9.466%   $231.4221   $231.42   $231.40   $231.40  
  Purchase #7 $67.63   12.370%   $75.9958   $76.00   $76.00   $76.00  
  7 purchase totals = $944.59       $1,017.4305   $1,017.43   $1,017.45   $1,017.50