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 $70.63   7.723%   $76.0848   $76.08   $76.10   $76.10  
  Purchase #2 $178.78   3.647%   $185.3001   $185.30   $185.30   $185.30  
  Purchase #3 $217.53   5.702%   $229.9336   $229.93   $229.95   $229.90  
  Purchase #4 $168.38   4.675%   $176.2518   $176.25   $176.25   $176.30  
  Purchase #5 $24.29   5.452%   $25.6143   $25.61   $25.60   $25.60  
  Purchase #6 $101.28   9.627%   $111.0302   $111.03   $111.05   $111.00  
  Purchase #7 $223.27   13.540%   $253.5008   $253.50   $253.50   $253.50  
  7 purchase totals = $984.16       $1,057.7156   $1,057.70   $1,057.75   $1,057.70