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 $61.45   3.749%   $63.7538   $63.75   $63.75   $63.80  
  Purchase #2 $243.73   10.735%   $269.8944   $269.89   $269.90   $269.90  
  Purchase #3 $23.80   7.360%   $25.5517   $25.55   $25.55   $25.60  
  Purchase #4 $31.77   5.630%   $33.5587   $33.56   $33.55   $33.60  
  Purchase #5 $230.85   10.340%   $254.7199   $254.72   $254.70   $254.70  
  Purchase #6 $116.37   11.829%   $130.1354   $130.14   $130.15   $130.10  
  Purchase #7 $163.74   8.280%   $177.2977   $177.30   $177.30   $177.30  
  7 purchase totals = $871.71       $954.9116   $954.91   $954.90   $955.00