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 $23.51   5.807%   $24.8752   $24.88   $24.90   $24.90  
  Purchase #2 $227.34   10.419%   $251.0266   $251.03   $251.05   $251.00  
  Purchase #3 $24.40   9.709%   $26.769   $26.77   $26.75   $26.80  
  Purchase #4 $48.26   9.792%   $52.9856   $52.99   $53.00   $53.00  
  Purchase #5 $63.94   9.525%   $70.0303   $70.03   $70.05   $70.00  
  Purchase #6 $77.59   5.321%   $81.7186   $81.72   $81.70   $81.70  
  Purchase #7 $231.73   13.745%   $263.5813   $263.58   $263.60   $263.60  
  7 purchase totals = $696.77       $770.9866   $771.00   $771.05   $771.00