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 $181.88   13.675%   $206.7521   $206.75   $206.75   $206.80  
  Purchase #2 $88.57   5.651%   $93.5751   $93.58   $93.60   $93.60  
  Purchase #3 $116.32   9.273%   $127.1064   $127.11   $127.10   $127.10  
  Purchase #4 $227.36   8.151%   $245.8921   $245.89   $245.90   $245.90  
  Purchase #5 $84.72   7.832%   $91.3553   $91.36   $91.35   $91.40  
  Purchase #6 $237.70   12.109%   $266.4831   $266.48   $266.50   $266.50  
  Purchase #7 $237.59   11.402%   $264.68   $264.68   $264.70   $264.70  
  7 purchase totals = $1,174.14       $1,295.8441   $1,295.85   $1,295.90   $1,296.00