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 $22.97   11.345%   $25.5759   $25.58   $25.60   $25.60  
  Purchase #2 $140.39   6.255%   $149.1714   $149.17   $149.15   $149.20  
  Purchase #3 $144.29   3.170%   $148.864   $148.86   $148.85   $148.90  
  Purchase #4 $189.85   8.509%   $206.0043   $206.00   $206.00   $206.00  
  Purchase #5 $35.35   13.355%   $40.071   $40.07   $40.05   $40.10  
  Purchase #6 $198.99   8.282%   $215.4704   $215.47   $215.45   $215.50  
  Purchase #7 $26.79   9.415%   $29.3123   $29.31   $29.30   $29.30  
  7 purchase totals = $758.63       $814.4693   $814.46   $814.40   $814.60