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 $229.81   10.356%   $253.6091   $253.61   $253.60   $253.60  
  Purchase #2 $10.75   4.283%   $11.2104   $11.21   $11.20   $11.20  
  Purchase #3 $74.39   3.130%   $76.7184   $76.72   $76.70   $76.70  
  Purchase #4 $80.83   4.337%   $84.3356   $84.34   $84.35   $84.30  
  Purchase #5 $119.93   12.102%   $134.4439   $134.44   $134.45   $134.40  
  Purchase #6 $113.39   11.665%   $126.6169   $126.62   $126.60   $126.60  
  Purchase #7 $59.73   8.487%   $64.7993   $64.80   $64.80   $64.80  
  7 purchase totals = $688.83       $751.7336   $751.74   $751.70   $751.60