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 $240.77   3.273%   $248.6504   $248.65   $248.65   $248.70  
  Purchase #2 $204.93   3.757%   $212.6292   $212.63   $212.65   $212.60  
  Purchase #3 $164.96   4.430%   $172.2677   $172.27   $172.25   $172.30  
  Purchase #4 $154.31   13.782%   $175.577   $175.58   $175.60   $175.60  
  Purchase #5 $111.89   13.457%   $126.947   $126.95   $126.95   $126.90  
  Purchase #6 $85.40   9.738%   $93.7163   $93.72   $93.70   $93.70  
  Purchase #7 $20.31   7.518%   $21.8369   $21.84   $21.85   $21.80  
  7 purchase totals = $982.57       $1,051.6245   $1,051.64   $1,051.65   $1,051.60