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 $164.37   13.364%   $186.3364   $186.34   $186.35   $186.30  
  Purchase #2 $118.26   9.382%   $129.3552   $129.36   $129.35   $129.40  
  Purchase #3 $47.67   9.217%   $52.0637   $52.06   $52.05   $52.10  
  Purchase #4 $203.68   10.359%   $224.7792   $224.78   $224.80   $224.80  
  Purchase #5 $160.38   8.569%   $174.123   $174.12   $174.10   $174.10  
  Purchase #6 $85.38   4.328%   $89.0752   $89.08   $89.10   $89.10  
  Purchase #7 $52.90   6.684%   $56.4358   $56.44   $56.45   $56.40  
  7 purchase totals = $832.64       $912.1685   $912.18   $912.20   $912.20