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 $71.54   7.209%   $76.6973   $76.70   $76.70   $76.70  
  Purchase #2 $187.48   8.359%   $203.1515   $203.15   $203.15   $203.20  
  Purchase #3 $224.95   10.661%   $248.9319   $248.93   $248.95   $248.90  
  Purchase #4 $136.90   6.718%   $146.0969   $146.10   $146.10   $146.10  
  Purchase #5 $85.71   6.435%   $91.2254   $91.23   $91.25   $91.20  
  Purchase #6 $155.70   7.284%   $167.0412   $167.04   $167.05   $167.00  
  Purchase #7 $225.33   3.716%   $233.7033   $233.70   $233.70   $233.70  
  7 purchase totals = $1,087.61       $1,166.8475   $1,166.85   $1,166.90   $1,166.80