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 $87.48   12.253%   $98.1989   $98.20   $98.20   $98.20  
  Purchase #2 $247.83   10.469%   $273.7753   $273.78   $273.80   $273.80  
  Purchase #3 $241.65   13.457%   $274.1688   $274.17   $274.15   $274.20  
  Purchase #4 $218.60   12.554%   $246.043   $246.04   $246.05   $246.00  
  Purchase #5 $135.76   12.139%   $152.2399   $152.24   $152.25   $152.20  
  Purchase #6 $23.34   4.723%   $24.4423   $24.44   $24.45   $24.40  
  Purchase #7 $150.60   10.748%   $166.7865   $166.79   $166.80   $166.80  
  7 purchase totals = $1,105.26       $1,235.6547   $1,235.66   $1,235.70   $1,235.60