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 $205.75   13.571%   $233.6723   $233.67   $233.65   $233.70  
  Purchase #2 $130.57   10.509%   $144.2916   $144.29   $144.30   $144.30  
  Purchase #3 $81.41   3.406%   $84.1828   $84.18   $84.20   $84.20  
  Purchase #4 $74.86   3.628%   $77.5759   $77.58   $77.60   $77.60  
  Purchase #5 $105.33   9.744%   $115.5934   $115.59   $115.60   $115.60  
  Purchase #6 $60.69   9.684%   $66.5672   $66.57   $66.55   $66.60  
  Purchase #7 $17.83   12.639%   $20.0835   $20.08   $20.10   $20.10  
  7 purchase totals = $676.44       $741.9667   $741.96   $742.00   $742.10