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 $24.26   6.200%   $25.7641   $25.76   $25.75   $25.80  
  Purchase #2 $82.69   10.824%   $91.6404   $91.64   $91.65   $91.60  
  Purchase #3 $243.75   11.423%   $271.5936   $271.59   $271.60   $271.60  
  Purchase #4 $248.28   10.740%   $274.9453   $274.95   $274.95   $274.90  
  Purchase #5 $215.63   13.645%   $245.0527   $245.05   $245.05   $245.10  
  Purchase #6 $235.88   5.417%   $248.6576   $248.66   $248.65   $248.70  
  Purchase #7 $53.36   11.566%   $59.5316   $59.53   $59.55   $59.50  
  7 purchase totals = $1,103.85       $1,217.1853   $1,217.18   $1,217.20   $1,217.20