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 $63.49   6.333%   $67.5108   $67.51   $67.50   $67.50  
  Purchase #2 $242.98   13.867%   $276.674   $276.67   $276.65   $276.70  
  Purchase #3 $47.46   13.667%   $53.9464   $53.95   $53.95   $53.90  
  Purchase #4 $61.83   3.529%   $64.012   $64.01   $64.00   $64.00  
  Purchase #5 $54.49   4.169%   $56.7617   $56.76   $56.75   $56.80  
  Purchase #6 $212.99   9.717%   $233.6862   $233.69   $233.70   $233.70  
  Purchase #7 $223.46   11.259%   $248.6194   $248.62   $248.60   $248.60  
  7 purchase totals = $906.70       $1,001.2105   $1,001.21   $1,001.15   $1,001.20