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 $22.47   10.794%   $24.8954   $24.90   $24.90   $24.90  
  Purchase #2 $110.90   11.859%   $124.0516   $124.05   $124.05   $124.10  
  Purchase #3 $68.38   8.528%   $74.2114   $74.21   $74.20   $74.20  
  Purchase #4 $176.61   4.564%   $184.6705   $184.67   $184.65   $184.70  
  Purchase #5 $10.70   7.315%   $11.4827   $11.48   $11.50   $11.50  
  Purchase #6 $200.84   3.784%   $208.4398   $208.44   $208.45   $208.40  
  Purchase #7 $111.68   6.442%   $118.8744   $118.87   $118.85   $118.90  
  7 purchase totals = $701.58       $746.6258   $746.62   $746.60   $746.70