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 $49.86   10.247%   $54.9692   $54.97   $54.95   $55.00  
  Purchase #2 $162.72   13.517%   $184.7149   $184.71   $184.70   $184.70  
  Purchase #3 $219.51   6.404%   $233.5674   $233.57   $233.55   $233.60  
  Purchase #4 $154.47   12.150%   $173.2381   $173.24   $173.25   $173.20  
  Purchase #5 $113.95   10.360%   $125.7552   $125.76   $125.75   $125.80  
  Purchase #6 $42.28   9.174%   $46.1588   $46.16   $46.15   $46.20  
  Purchase #7 $232.94   6.663%   $248.4608   $248.46   $248.45   $248.50  
  7 purchase totals = $975.73       $1,066.8644   $1,066.87   $1,066.80   $1,067.00