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 $204.67   13.831%   $232.9779   $232.98   $233.00   $233.00  
  Purchase #2 $134.76   5.414%   $142.0559   $142.06   $142.05   $142.10  
  Purchase #3 $233.33   8.641%   $253.492   $253.49   $253.50   $253.50  
  Purchase #4 $217.49   13.797%   $247.4971   $247.50   $247.50   $247.50  
  Purchase #5 $52.54   4.106%   $54.6973   $54.70   $54.70   $54.70  
  Purchase #6 $101.71   12.420%   $114.3424   $114.34   $114.35   $114.30  
  Purchase #7 $238.33   5.198%   $250.7184   $250.72   $250.70   $250.70  
  7 purchase totals = $1,182.83       $1,295.7810   $1,295.79   $1,295.80   $1,295.80