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 $247.52   7.868%   $266.9949   $266.99   $267.00   $267.00  
  Purchase #2 $215.79   11.165%   $239.883   $239.88   $239.90   $239.90  
  Purchase #3 $46.80   6.751%   $49.9595   $49.96   $49.95   $50.00  
  Purchase #4 $245.41   9.495%   $268.7117   $268.71   $268.70   $268.70  
  Purchase #5 $113.59   3.441%   $117.4986   $117.50   $117.50   $117.50  
  Purchase #6 $164.43   12.260%   $184.5891   $184.59   $184.60   $184.60  
  Purchase #7 $132.26   8.664%   $143.719   $143.72   $143.70   $143.70  
  7 purchase totals = $1,165.80       $1,271.3558   $1,271.35   $1,271.35   $1,271.40