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 $145.43   7.582%   $156.4565   $156.46   $156.45   $156.50  
  Purchase #2 $226.74   8.373%   $245.7249   $245.72   $245.70   $245.70  
  Purchase #3 $181.93   3.669%   $188.605   $188.61   $188.60   $188.60  
  Purchase #4 $246.45   4.832%   $258.3585   $258.36   $258.35   $258.40  
  Purchase #5 $184.54   13.439%   $209.3403   $209.34   $209.35   $209.30  
  Purchase #6 $111.97   6.462%   $119.2055   $119.21   $119.20   $119.20  
  Purchase #7 $155.87   6.597%   $166.1527   $166.15   $166.15   $166.20  
  7 purchase totals = $1,252.93       $1,343.8434   $1,343.85   $1,343.80   $1,343.90