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 $55.38   13.808%   $63.0269   $63.03   $63.05   $63.00  
  Purchase #2 $117.35   5.717%   $124.0589   $124.06   $124.05   $124.10  
  Purchase #3 $60.49   3.696%   $62.7257   $62.73   $62.75   $62.70  
  Purchase #4 $208.90   8.566%   $226.7944   $226.79   $226.80   $226.80  
  Purchase #5 $35.53   3.135%   $36.6439   $36.64   $36.65   $36.60  
  Purchase #6 $197.83   11.207%   $220.0008   $220.00   $220.00   $220.00  
  Purchase #7 $238.89   11.580%   $266.5535   $266.55   $266.55   $266.60  
  7 purchase totals = $914.37       $999.8041   $999.80   $999.85   $999.80