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 $23.91   8.581%   $25.9617   $25.96   $25.95   $26.00  
  Purchase #2 $175.69   4.696%   $183.9404   $183.94   $183.95   $183.90  
  Purchase #3 $87.38   3.794%   $90.6952   $90.70   $90.70   $90.70  
  Purchase #4 $209.74   8.661%   $227.9056   $227.91   $227.90   $227.90  
  Purchase #5 $38.72   11.611%   $43.2158   $43.22   $43.20   $43.20  
  Purchase #6 $166.82   9.386%   $182.4777   $182.48   $182.50   $182.50  
  Purchase #7 $202.93   4.569%   $212.2019   $212.20   $212.20   $212.20  
  7 purchase totals = $905.19       $966.3983   $966.41   $966.40   $966.40