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 $144.42   13.527%   $163.9557   $163.96   $163.95   $164.00  
  Purchase #2 $227.51   9.667%   $249.5034   $249.50   $249.50   $249.50  
  Purchase #3 $74.99   11.827%   $83.8591   $83.86   $83.85   $83.90  
  Purchase #4 $175.54   9.102%   $191.5177   $191.52   $191.50   $191.50  
  Purchase #5 $171.81   11.339%   $191.2915   $191.29   $191.30   $191.30  
  Purchase #6 $136.35   6.627%   $145.3859   $145.39   $145.40   $145.40  
  Purchase #7 $249.63   8.247%   $270.217   $270.22   $270.20   $270.20  
  7 purchase totals = $1,180.25       $1,295.7303   $1,295.74   $1,295.70   $1,295.80