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 $184.81   12.470%   $207.8558   $207.86   $207.85   $207.90  
  Purchase #2 $243.81   11.430%   $271.6775   $271.68   $271.70   $271.70  
  Purchase #3 $164.91   9.457%   $180.5055   $180.51   $180.50   $180.50  
  Purchase #4 $43.41   8.339%   $47.03   $47.03   $47.05   $47.00  
  Purchase #5 $157.48   13.215%   $178.291   $178.29   $178.30   $178.30  
  Purchase #6 $160.53   8.750%   $174.5764   $174.58   $174.60   $174.60  
  Purchase #7 $51.28   5.469%   $54.0845   $54.08   $54.10   $54.10  
  7 purchase totals = $1,006.23       $1,114.0207   $1,114.03   $1,114.10   $1,114.10