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 $114.67   3.205%   $118.3452   $118.35   $118.35   $118.30  
  Purchase #2 $46.76   5.651%   $49.4024   $49.40   $49.40   $49.40  
  Purchase #3 $51.29   7.701%   $55.2398   $55.24   $55.25   $55.20  
  Purchase #4 $92.51   4.689%   $96.8478   $96.85   $96.85   $96.80  
  Purchase #5 $244.57   12.841%   $275.9752   $275.98   $276.00   $276.00  
  Purchase #6 $17.41   3.736%   $18.0604   $18.06   $18.05   $18.10  
  Purchase #7 $90.93   4.247%   $94.7918   $94.79   $94.80   $94.80  
  7 purchase totals = $658.14       $708.6626   $708.67   $708.70   $708.60