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 $57.40   11.177%   $63.8156   $63.82   $63.80   $63.80  
  Purchase #2 $119.58   7.575%   $128.6382   $128.64   $128.65   $128.60  
  Purchase #3 $211.62   12.637%   $238.3624   $238.36   $238.35   $238.40  
  Purchase #4 $100.45   12.701%   $113.2082   $113.21   $113.20   $113.20  
  Purchase #5 $172.86   3.371%   $178.6871   $178.69   $178.70   $178.70  
  Purchase #6 $36.71   11.659%   $40.99   $40.99   $41.00   $41.00  
  Purchase #7 $115.53   3.515%   $119.5909   $119.59   $119.60   $119.60  
  7 purchase totals = $814.15       $883.2924   $883.30   $883.30   $883.30