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 $57.90   6.808%   $61.8418   $61.84   $61.85   $61.80  
  Purchase #2 $159.83   13.151%   $180.8492   $180.85   $180.85   $180.80  
  Purchase #3 $242.44   8.526%   $263.1104   $263.11   $263.10   $263.10  
  Purchase #4 $117.84   10.326%   $130.0082   $130.01   $130.00   $130.00  
  Purchase #5 $110.77   3.200%   $114.3146   $114.31   $114.30   $114.30  
  Purchase #6 $84.64   4.525%   $88.47   $88.47   $88.45   $88.50  
  Purchase #7 $161.39   6.365%   $171.6625   $171.66   $171.65   $171.70  
  7 purchase totals = $934.81       $1,010.2567   $1,010.25   $1,010.20   $1,010.20