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 $85.97   12.777%   $96.9544   $96.95   $96.95   $97.00  
  Purchase #2 $48.26   13.775%   $54.9078   $54.91   $54.90   $54.90  
  Purchase #3 $82.66   11.274%   $91.9791   $91.98   $92.00   $92.00  
  Purchase #4 $140.53   13.291%   $159.2078   $159.21   $159.20   $159.20  
  Purchase #5 $83.98   3.228%   $86.6909   $86.69   $86.70   $86.70  
  Purchase #6 $176.33   8.196%   $190.782   $190.78   $190.80   $190.80  
  Purchase #7 $90.80   5.711%   $95.9856   $95.99   $96.00   $96.00  
  7 purchase totals = $708.53       $776.5076   $776.51   $776.55   $776.60