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 $181.49   7.715%   $195.492   $195.49   $195.50   $195.50  
  Purchase #2 $197.84   13.587%   $224.7205   $224.72   $224.70   $224.70  
  Purchase #3 $15.83   11.236%   $17.6087   $17.61   $17.60   $17.60  
  Purchase #4 $171.39   13.704%   $194.8773   $194.88   $194.90   $194.90  
  Purchase #5 $106.74   12.256%   $119.8221   $119.82   $119.80   $119.80  
  Purchase #6 $230.90   10.751%   $255.7241   $255.72   $255.70   $255.70  
  Purchase #7 $73.85   3.313%   $76.2967   $76.30   $76.30   $76.30  
  7 purchase totals = $978.04       $1,084.5414   $1,084.54   $1,084.50   $1,084.50