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 $62.54   8.566%   $67.8972   $67.90   $67.90   $67.90  
  Purchase #2 $78.65   11.787%   $87.9205   $87.92   $87.90   $87.90  
  Purchase #3 $227.95   9.197%   $248.9146   $248.91   $248.90   $248.90  
  Purchase #4 $131.34   11.254%   $146.121   $146.12   $146.10   $146.10  
  Purchase #5 $210.64   8.206%   $227.9251   $227.93   $227.95   $227.90  
  Purchase #6 $186.74   3.619%   $193.4981   $193.50   $193.50   $193.50  
  Purchase #7 $47.43   10.351%   $52.3395   $52.34   $52.35   $52.30  
  7 purchase totals = $945.29       $1,024.6160   $1,024.62   $1,024.60   $1,024.50