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 $38.84   10.809%   $43.0382   $43.04   $43.05   $43.00  
  Purchase #2 $235.63   13.495%   $267.4283   $267.43   $267.45   $267.40  
  Purchase #3 $248.91   5.602%   $262.8539   $262.85   $262.85   $262.90  
  Purchase #4 $80.64   10.785%   $89.337   $89.34   $89.35   $89.30  
  Purchase #5 $221.76   4.761%   $232.318   $232.32   $232.30   $232.30  
  Purchase #6 $213.47   7.727%   $229.9648   $229.96   $229.95   $230.00  
  Purchase #7 $98.99   6.657%   $105.5798   $105.58   $105.60   $105.60  
  7 purchase totals = $1,138.24       $1,230.5200   $1,230.52   $1,230.55   $1,230.50