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 $58.75   3.548%   $60.8345   $60.83   $60.85   $60.80  
  Purchase #2 $24.47   7.416%   $26.2847   $26.28   $26.30   $26.30  
  Purchase #3 $151.58   9.385%   $165.8058   $165.81   $165.80   $165.80  
  Purchase #4 $204.43   5.858%   $216.4055   $216.41   $216.40   $216.40  
  Purchase #5 $194.56   4.176%   $202.6848   $202.68   $202.70   $202.70  
  Purchase #6 $17.38   10.311%   $19.1721   $19.17   $19.15   $19.20  
  Purchase #7 $83.25   9.631%   $91.2678   $91.27   $91.25   $91.30  
  7 purchase totals = $734.42       $782.4552   $782.45   $782.45   $782.50