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 $62.39   11.133%   $69.3359   $69.34   $69.35   $69.30  
  Purchase #2 $17.49   10.502%   $19.3268   $19.33   $19.35   $19.30  
  Purchase #3 $154.76   13.865%   $176.2175   $176.22   $176.20   $176.20  
  Purchase #4 $239.41   13.740%   $272.3049   $272.30   $272.30   $272.30  
  Purchase #5 $80.63   4.803%   $84.5027   $84.50   $84.50   $84.50  
  Purchase #6 $166.36   3.426%   $172.0595   $172.06   $172.05   $172.10  
  Purchase #7 $180.35   12.359%   $202.6395   $202.64   $202.65   $202.60  
  7 purchase totals = $901.39       $996.3868   $996.39   $996.40   $996.30