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 $194.40   6.261%   $206.5714   $206.57   $206.55   $206.60  
  Purchase #2 $171.63   6.150%   $182.1852   $182.19   $182.20   $182.20  
  Purchase #3 $214.74   8.268%   $232.4947   $232.49   $232.50   $232.50  
  Purchase #4 $149.95   12.858%   $169.2306   $169.23   $169.25   $169.20  
  Purchase #5 $49.47   10.459%   $54.6441   $54.64   $54.65   $54.60  
  Purchase #6 $191.81   8.241%   $207.6171   $207.62   $207.60   $207.60  
  Purchase #7 $127.68   5.671%   $134.9207   $134.92   $134.90   $134.90  
  7 purchase totals = $1,099.68       $1,187.6638   $1,187.66   $1,187.65   $1,187.60