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 $244.89   8.375%   $265.3995   $265.40   $265.40   $265.40  
  Purchase #2 $246.99   10.845%   $273.7761   $273.78   $273.80   $273.80  
  Purchase #3 $53.31   13.267%   $60.3826   $60.38   $60.40   $60.40  
  Purchase #4 $200.41   7.699%   $215.8396   $215.84   $215.85   $215.80  
  Purchase #5 $9.28   5.605%   $9.8001   $9.80   $9.80   $9.80  
  Purchase #6 $145.60   4.563%   $152.2437   $152.24   $152.25   $152.20  
  Purchase #7 $46.73   8.106%   $50.5179   $50.52   $50.50   $50.50  
  7 purchase totals = $947.21       $1,027.9595   $1,027.96   $1,028.00   $1,027.90