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 $232.93   13.437%   $264.2288   $264.23   $264.25   $264.20  
  Purchase #2 $42.43   7.452%   $45.5919   $45.59   $45.60   $45.60  
  Purchase #3 $213.99   6.356%   $227.5912   $227.59   $227.60   $227.60  
  Purchase #4 $44.54   4.382%   $46.4917   $46.49   $46.50   $46.50  
  Purchase #5 $73.42   9.422%   $80.3376   $80.34   $80.35   $80.30  
  Purchase #6 $49.58   3.336%   $51.234   $51.23   $51.25   $51.20  
  Purchase #7 $245.36   8.434%   $266.0537   $266.05   $266.05   $266.10  
  7 purchase totals = $902.25       $981.5289   $981.52   $981.60   $981.50