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 $245.26   3.247%   $253.2236   $253.22   $253.20   $253.20  
  Purchase #2 $207.90   4.787%   $217.8522   $217.85   $217.85   $217.90  
  Purchase #3 $219.61   13.226%   $248.6556   $248.66   $248.65   $248.70  
  Purchase #4 $35.64   9.605%   $39.0632   $39.06   $39.05   $39.10  
  Purchase #5 $233.78   3.416%   $241.7659   $241.77   $241.75   $241.80  
  Purchase #6 $44.77   8.240%   $48.459   $48.46   $48.45   $48.50  
  Purchase #7 $212.76   5.154%   $223.7257   $223.73   $223.75   $223.70  
  7 purchase totals = $1,199.72       $1,272.7452   $1,272.75   $1,272.70   $1,272.90