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 $164.79   10.604%   $182.2643   $182.26   $182.25   $182.30  
  Purchase #2 $184.55   13.716%   $209.8629   $209.86   $209.85   $209.90  
  Purchase #3 $58.52   10.752%   $64.8121   $64.81   $64.80   $64.80  
  Purchase #4 $184.79   4.497%   $193.1   $193.10   $193.10   $193.10  
  Purchase #5 $211.88   13.438%   $240.3524   $240.35   $240.35   $240.40  
  Purchase #6 $219.64   5.677%   $232.109   $232.11   $232.10   $232.10  
  Purchase #7 $90.63   5.308%   $95.4406   $95.44   $95.45   $95.40  
  7 purchase totals = $1,114.80       $1,217.9413   $1,217.93   $1,217.90   $1,218.00