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 $126.47   6.496%   $134.6855   $134.69   $134.70   $134.70  
  Purchase #2 $97.79   12.133%   $109.6549   $109.65   $109.65   $109.70  
  Purchase #3 $245.61   4.791%   $257.3772   $257.38   $257.40   $257.40  
  Purchase #4 $197.73   11.364%   $220.2   $220.20   $220.20   $220.20  
  Purchase #5 $106.49   7.289%   $114.2521   $114.25   $114.25   $114.30  
  Purchase #6 $153.51   10.527%   $169.67   $169.67   $169.65   $169.70  
  Purchase #7 $237.81   4.532%   $248.5875   $248.59   $248.60   $248.60  
  7 purchase totals = $1,165.41       $1,254.4272   $1,254.43   $1,254.45   $1,254.60