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 $237.89   12.281%   $267.1053   $267.11   $267.10   $267.10  
  Purchase #2 $177.36   9.448%   $194.117   $194.12   $194.10   $194.10  
  Purchase #3 $199.88   3.173%   $206.2222   $206.22   $206.20   $206.20  
  Purchase #4 $22.88   7.518%   $24.6001   $24.60   $24.60   $24.60  
  Purchase #5 $171.76   7.820%   $185.1916   $185.19   $185.20   $185.20  
  Purchase #6 $230.66   12.202%   $258.8051   $258.81   $258.80   $258.80  
  Purchase #7 $63.69   6.167%   $67.6178   $67.62   $67.60   $67.60  
  7 purchase totals = $1,104.12       $1,203.6591   $1,203.67   $1,203.60   $1,203.60