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 $246.25   6.695%   $262.7364   $262.74   $262.75   $262.70  
  Purchase #2 $151.49   13.142%   $171.3988   $171.40   $171.40   $171.40  
  Purchase #3 $211.33   9.652%   $231.7276   $231.73   $231.75   $231.70  
  Purchase #4 $65.30   13.781%   $74.299   $74.30   $74.30   $74.30  
  Purchase #5 $109.34   7.152%   $117.16   $117.16   $117.15   $117.20  
  Purchase #6 $198.50   8.730%   $215.8291   $215.83   $215.85   $215.80  
  Purchase #7 $218.34   3.865%   $226.7788   $226.78   $226.80   $226.80  
  7 purchase totals = $1,200.55       $1,299.9297   $1,299.94   $1,300.00   $1,299.90