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 $136.98   7.248%   $146.9083   $146.91   $146.90   $146.90  
  Purchase #2 $223.91   6.635%   $238.7664   $238.77   $238.75   $238.80  
  Purchase #3 $80.58   6.717%   $85.9926   $85.99   $86.00   $86.00  
  Purchase #4 $182.99   5.470%   $192.9996   $193.00   $193.00   $193.00  
  Purchase #5 $45.60   13.359%   $51.6917   $51.69   $51.70   $51.70  
  Purchase #6 $38.68   11.794%   $43.2419   $43.24   $43.25   $43.20  
  Purchase #7 $223.53   13.493%   $253.6909   $253.69   $253.70   $253.70  
  7 purchase totals = $932.27       $1,013.2914   $1,013.29   $1,013.30   $1,013.30