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 $248.27   5.760%   $262.5704   $262.57   $262.55   $262.60  
  Purchase #2 $146.46   4.843%   $153.5531   $153.55   $153.55   $153.60  
  Purchase #3 $37.63   3.323%   $38.8804   $38.88   $38.90   $38.90  
  Purchase #4 $53.78   8.191%   $58.1851   $58.19   $58.20   $58.20  
  Purchase #5 $215.36   4.669%   $225.4152   $225.42   $225.40   $225.40  
  Purchase #6 $135.55   6.488%   $144.3445   $144.34   $144.35   $144.30  
  Purchase #7 $149.33   5.608%   $157.7044   $157.70   $157.70   $157.70  
  7 purchase totals = $986.38       $1,040.6531   $1,040.65   $1,040.65   $1,040.70