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 $81.36   8.508%   $88.2821   $88.28   $88.30   $88.30  
  Purchase #2 $216.73   7.290%   $232.5296   $232.53   $232.55   $232.50  
  Purchase #3 $52.49   8.313%   $56.8535   $56.85   $56.85   $56.90  
  Purchase #4 $239.86   12.800%   $270.5621   $270.56   $270.55   $270.60  
  Purchase #5 $167.81   4.115%   $174.7154   $174.72   $174.70   $174.70  
  Purchase #6 $79.26   8.645%   $86.112   $86.11   $86.10   $86.10  
  Purchase #7 $46.27   13.115%   $52.3383   $52.34   $52.35   $52.30  
  7 purchase totals = $883.78       $961.3930   $961.39   $961.40   $961.40