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 $204.50   3.329%   $211.3078   $211.31   $211.30   $211.30  
  Purchase #2 $239.45   13.689%   $272.2283   $272.23   $272.25   $272.20  
  Purchase #3 $59.77   10.198%   $65.8653   $65.87   $65.85   $65.90  
  Purchase #4 $108.99   9.754%   $119.6209   $119.62   $119.60   $119.60  
  Purchase #5 $151.54   8.649%   $164.6467   $164.65   $164.65   $164.60  
  Purchase #6 $67.69   9.408%   $74.0583   $74.06   $74.05   $74.10  
  Purchase #7 $141.79   12.711%   $159.8129   $159.81   $159.80   $159.80  
  7 purchase totals = $973.73       $1,067.5402   $1,067.55   $1,067.50   $1,067.50