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 $214.47   12.261%   $240.7662   $240.77   $240.75   $240.80  
  Purchase #2 $211.28   7.103%   $226.2872   $226.29   $226.30   $226.30  
  Purchase #3 $173.37   8.576%   $188.2382   $188.24   $188.25   $188.20  
  Purchase #4 $79.88   13.532%   $90.6894   $90.69   $90.70   $90.70  
  Purchase #5 $199.67   7.533%   $214.7111   $214.71   $214.70   $214.70  
  Purchase #6 $235.70   11.493%   $262.789   $262.79   $262.80   $262.80  
  Purchase #7 $46.93   11.564%   $52.357   $52.36   $52.35   $52.40  
  7 purchase totals = $1,161.30       $1,275.8381   $1,275.85   $1,275.85   $1,275.90