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 $144.89   11.195%   $161.1104   $161.11   $161.10   $161.10  
  Purchase #2 $153.98   12.574%   $173.3414   $173.34   $173.35   $173.30  
  Purchase #3 $60.55   3.783%   $62.8406   $62.84   $62.85   $62.80  
  Purchase #4 $176.69   5.214%   $185.9026   $185.90   $185.90   $185.90  
  Purchase #5 $186.92   10.137%   $205.8681   $205.87   $205.85   $205.90  
  Purchase #6 $171.43   12.582%   $192.9993   $193.00   $193.00   $193.00  
  Purchase #7 $76.69   5.105%   $80.605   $80.61   $80.60   $80.60  
  7 purchase totals = $971.15       $1,062.6674   $1,062.67   $1,062.65   $1,062.60