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 $86.30   10.755%   $95.5816   $95.58   $95.60   $95.60  
  Purchase #2 $157.53   11.192%   $175.1608   $175.16   $175.15   $175.20  
  Purchase #3 $170.76   4.739%   $178.8523   $178.85   $178.85   $178.90  
  Purchase #4 $193.95   3.689%   $201.1048   $201.10   $201.10   $201.10  
  Purchase #5 $233.83   3.529%   $242.0819   $242.08   $242.10   $242.10  
  Purchase #6 $233.38   10.326%   $257.4788   $257.48   $257.50   $257.50  
  Purchase #7 $88.59   12.745%   $99.8808   $99.88   $99.90   $99.90  
  7 purchase totals = $1,164.34       $1,250.1410   $1,250.13   $1,250.20   $1,250.30