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 $113.56   8.463%   $123.1706   $123.17   $123.15   $123.20  
  Purchase #2 $57.99   13.359%   $65.7369   $65.74   $65.75   $65.70  
  Purchase #3 $239.36   5.501%   $252.5272   $252.53   $252.55   $252.50  
  Purchase #4 $230.53   7.483%   $247.7806   $247.78   $247.80   $247.80  
  Purchase #5 $113.48   5.261%   $119.4502   $119.45   $119.45   $119.50  
  Purchase #6 $79.83   6.705%   $85.1826   $85.18   $85.20   $85.20  
  Purchase #7 $229.98   7.623%   $247.5114   $247.51   $247.50   $247.50  
  7 purchase totals = $1,064.73       $1,141.3595   $1,141.36   $1,141.40   $1,141.40