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 $235.51   11.179%   $261.8377   $261.84   $261.85   $261.80  
  Purchase #2 $138.86   6.801%   $148.3039   $148.30   $148.30   $148.30  
  Purchase #3 $127.72   6.452%   $135.9605   $135.96   $135.95   $136.00  
  Purchase #4 $100.48   5.487%   $105.9933   $105.99   $106.00   $106.00  
  Purchase #5 $140.36   12.306%   $157.6327   $157.63   $157.65   $157.60  
  Purchase #6 $88.67   8.544%   $96.246   $96.25   $96.25   $96.20  
  Purchase #7 $234.25   13.232%   $265.246   $265.25   $265.25   $265.20  
  7 purchase totals = $1,065.85       $1,171.2201   $1,171.22   $1,171.25   $1,171.10