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 $61.80   3.163%   $63.7547   $63.75   $63.75   $63.80  
  Purchase #2 $47.94   7.167%   $51.3759   $51.38   $51.40   $51.40  
  Purchase #3 $118.59   10.301%   $130.806   $130.81   $130.80   $130.80  
  Purchase #4 $211.62   11.811%   $236.6144   $236.61   $236.60   $236.60  
  Purchase #5 $19.60   11.480%   $21.8501   $21.85   $21.85   $21.90  
  Purchase #6 $24.35   8.536%   $26.4285   $26.43   $26.45   $26.40  
  Purchase #7 $211.32   3.820%   $219.3924   $219.39   $219.40   $219.40  
  7 purchase totals = $695.22       $750.2220   $750.22   $750.25   $750.30