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 $113.40   11.539%   $126.4852   $126.49   $126.50   $126.50  
  Purchase #2 $166.64   12.181%   $186.9384   $186.94   $186.95   $186.90  
  Purchase #3 $184.69   7.289%   $198.1521   $198.15   $198.15   $198.20  
  Purchase #4 $183.97   7.550%   $197.8597   $197.86   $197.85   $197.90  
  Purchase #5 $151.66   4.352%   $158.2602   $158.26   $158.25   $158.30  
  Purchase #6 $64.60   8.353%   $69.996   $70.00   $70.00   $70.00  
  Purchase #7 $58.74   7.506%   $63.149   $63.15   $63.15   $63.10  
  7 purchase totals = $923.70       $1,000.8406   $1,000.85   $1,000.85   $1,000.90