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 $206.58   7.299%   $221.6583   $221.66   $221.65   $221.70  
  Purchase #2 $124.42   8.677%   $135.2159   $135.22   $135.20   $135.20  
  Purchase #3 $204.34   10.712%   $226.2289   $226.23   $226.25   $226.20  
  Purchase #4 $40.81   5.635%   $43.1096   $43.11   $43.10   $43.10  
  Purchase #5 $121.27   3.108%   $125.0391   $125.04   $125.05   $125.00  
  Purchase #6 $94.81   7.502%   $101.9226   $101.92   $101.90   $101.90  
  Purchase #7 $120.53   8.668%   $130.9775   $130.98   $131.00   $131.00  
  7 purchase totals = $912.76       $984.1519   $984.16   $984.15   $984.10