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 $246.89   5.458%   $260.3653   $260.37   $260.35   $260.40  
  Purchase #2 $46.94   5.656%   $49.5949   $49.59   $49.60   $49.60  
  Purchase #3 $24.78   5.638%   $26.1771   $26.18   $26.20   $26.20  
  Purchase #4 $47.40   13.635%   $53.863   $53.86   $53.85   $53.90  
  Purchase #5 $186.62   8.488%   $202.4603   $202.46   $202.45   $202.50  
  Purchase #6 $233.36   3.809%   $242.2487   $242.25   $242.25   $242.20  
  Purchase #7 $209.51   11.420%   $233.436   $233.44   $233.45   $233.40  
  7 purchase totals = $995.50       $1,068.1453   $1,068.15   $1,068.15   $1,068.20