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 $155.47   11.761%   $173.7548   $173.75   $173.75   $173.80  
  Purchase #2 $238.83   13.705%   $271.5617   $271.56   $271.55   $271.60  
  Purchase #3 $226.29   3.721%   $234.7103   $234.71   $234.70   $234.70  
  Purchase #4 $55.56   10.455%   $61.3688   $61.37   $61.35   $61.40  
  Purchase #5 $247.88   13.501%   $281.3463   $281.35   $281.35   $281.30  
  Purchase #6 $164.70   13.680%   $187.231   $187.23   $187.25   $187.20  
  Purchase #7 $6.94   9.280%   $7.584   $7.58   $7.60   $7.60  
  7 purchase totals = $1,095.67       $1,217.5569   $1,217.55   $1,217.55   $1,217.60