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 $164.60   10.632%   $182.1003   $182.10   $182.10   $182.10  
  Purchase #2 $230.75   11.754%   $257.8724   $257.87   $257.85   $257.90  
  Purchase #3 $12.46   8.562%   $13.5268   $13.53   $13.55   $13.50  
  Purchase #4 $68.36   9.318%   $74.7298   $74.73   $74.75   $74.70  
  Purchase #5 $88.49   11.521%   $98.6849   $98.68   $98.70   $98.70  
  Purchase #6 $169.32   6.203%   $179.8229   $179.82   $179.80   $179.80  
  Purchase #7 $180.83   7.702%   $194.7575   $194.76   $194.75   $194.80  
  7 purchase totals = $914.81       $1,001.4946   $1,001.49   $1,001.50   $1,001.50