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 $59.25   7.307%   $63.5794   $63.58   $63.60   $63.60  
  Purchase #2 $185.90   8.493%   $201.6885   $201.69   $201.70   $201.70  
  Purchase #3 $236.99   4.530%   $247.7256   $247.73   $247.75   $247.70  
  Purchase #4 $85.57   4.151%   $89.122   $89.12   $89.10   $89.10  
  Purchase #5 $220.81   8.522%   $239.6274   $239.63   $239.65   $239.60  
  Purchase #6 $186.85   10.199%   $205.9068   $205.91   $205.90   $205.90  
  Purchase #7 $83.71   11.250%   $93.1274   $93.13   $93.15   $93.10  
  7 purchase totals = $1,059.08       $1,140.7771   $1,140.79   $1,140.85   $1,140.70