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 $131.37   10.335%   $144.9471   $144.95   $144.95   $144.90  
  Purchase #2 $177.30   12.198%   $198.9271   $198.93   $198.95   $198.90  
  Purchase #3 $248.93   11.182%   $276.7654   $276.77   $276.75   $276.80  
  Purchase #4 $167.39   5.358%   $176.3588   $176.36   $176.35   $176.40  
  Purchase #5 $125.39   10.229%   $138.2161   $138.22   $138.20   $138.20  
  Purchase #6 $25.76   4.483%   $26.9148   $26.91   $26.90   $26.90  
  Purchase #7 $92.77   8.431%   $100.5914   $100.59   $100.60   $100.60  
  7 purchase totals = $968.91       $1,062.7207   $1,062.73   $1,062.70   $1,062.70