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 $92.79   4.116%   $96.6092   $96.61   $96.60   $96.60  
  Purchase #2 $47.65   7.278%   $51.118   $51.12   $51.10   $51.10  
  Purchase #3 $117.91   5.663%   $124.5872   $124.59   $124.60   $124.60  
  Purchase #4 $63.53   9.786%   $69.747   $69.75   $69.75   $69.70  
  Purchase #5 $230.61   9.868%   $253.3666   $253.37   $253.35   $253.40  
  Purchase #6 $163.87   11.605%   $182.8871   $182.89   $182.90   $182.90  
  Purchase #7 $60.45   11.206%   $67.224   $67.22   $67.20   $67.20  
  7 purchase totals = $776.81       $845.5391   $845.55   $845.50   $845.50