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 $69.48   8.391%   $75.3101   $75.31   $75.30   $75.30  
  Purchase #2 $76.47   12.474%   $86.0089   $86.01   $86.00   $86.00  
  Purchase #3 $52.37   8.621%   $56.8848   $56.88   $56.90   $56.90  
  Purchase #4 $77.33   10.625%   $85.5463   $85.55   $85.55   $85.50  
  Purchase #5 $196.49   13.267%   $222.5583   $222.56   $222.55   $222.60  
  Purchase #6 $247.55   6.480%   $263.5912   $263.59   $263.60   $263.60  
  Purchase #7 $163.66   5.749%   $173.0688   $173.07   $173.05   $173.10  
  7 purchase totals = $883.35       $962.9684   $962.97   $962.95   $963.00