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 $83.69   12.263%   $93.9529   $93.95   $93.95   $94.00  
  Purchase #2 $246.43   5.354%   $259.6239   $259.62   $259.60   $259.60  
  Purchase #3 $98.48   10.832%   $109.1474   $109.15   $109.15   $109.10  
  Purchase #4 $81.36   7.536%   $87.4913   $87.49   $87.50   $87.50  
  Purchase #5 $224.40   13.329%   $254.3103   $254.31   $254.30   $254.30  
  Purchase #6 $106.99   3.629%   $110.8727   $110.87   $110.85   $110.90  
  Purchase #7 $90.46   8.689%   $98.3201   $98.32   $98.30   $98.30  
  7 purchase totals = $931.81       $1,013.7186   $1,013.71   $1,013.65   $1,013.70