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 $127.77   5.454%   $134.7386   $134.74   $134.75   $134.70  
  Purchase #2 $177.81   9.604%   $194.8869   $194.89   $194.90   $194.90  
  Purchase #3 $11.80   9.551%   $12.927   $12.93   $12.95   $12.90  
  Purchase #4 $115.35   8.213%   $124.8237   $124.82   $124.80   $124.80  
  Purchase #5 $136.98   5.131%   $144.0084   $144.01   $144.00   $144.00  
  Purchase #6 $156.75   10.400%   $173.052   $173.05   $173.05   $173.10  
  Purchase #7 $157.93   5.264%   $166.2434   $166.24   $166.25   $166.20  
  7 purchase totals = $884.39       $950.6800   $950.68   $950.70   $950.60