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 $246.53   11.463%   $274.7897   $274.79   $274.80   $274.80  
  Purchase #2 $67.89   13.296%   $76.9167   $76.92   $76.90   $76.90  
  Purchase #3 $175.27   7.548%   $188.4994   $188.50   $188.50   $188.50  
  Purchase #4 $41.59   7.449%   $44.688   $44.69   $44.70   $44.70  
  Purchase #5 $145.85   7.511%   $156.8048   $156.80   $156.80   $156.80  
  Purchase #6 $213.69   8.791%   $232.4755   $232.48   $232.50   $232.50  
  Purchase #7 $149.49   3.670%   $154.9763   $154.98   $155.00   $155.00  
  7 purchase totals = $1,040.31       $1,129.1504   $1,129.16   $1,129.20   $1,129.20