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 $101.25   6.331%   $107.6601   $107.66   $107.65   $107.70  
  Purchase #2 $214.90   4.806%   $225.2281   $225.23   $225.25   $225.20  
  Purchase #3 $211.93   11.310%   $235.8993   $235.90   $235.90   $235.90  
  Purchase #4 $166.75   5.508%   $175.9346   $175.93   $175.95   $175.90  
  Purchase #5 $241.72   3.737%   $250.7531   $250.75   $250.75   $250.80  
  Purchase #6 $107.74   4.718%   $112.8232   $112.82   $112.80   $112.80  
  Purchase #7 $124.71   13.783%   $141.8988   $141.90   $141.90   $141.90  
  7 purchase totals = $1,169.00       $1,250.1972   $1,250.19   $1,250.20   $1,250.20