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 $62.58   7.653%   $67.3692   $67.37   $67.35   $67.40  
  Purchase #2 $235.85   11.596%   $263.1992   $263.20   $263.20   $263.20  
  Purchase #3 $38.44   10.497%   $42.475   $42.48   $42.50   $42.50  
  Purchase #4 $65.55   13.509%   $74.4051   $74.41   $74.40   $74.40  
  Purchase #5 $121.40   3.645%   $125.825   $125.83   $125.85   $125.80  
  Purchase #6 $248.82   3.575%   $257.7153   $257.72   $257.70   $257.70  
  Purchase #7 $208.46   13.769%   $237.1629   $237.16   $237.15   $237.20  
  7 purchase totals = $981.10       $1,068.1517   $1,068.17   $1,068.15   $1,068.20