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 $85.30   13.705%   $96.9904   $96.99   $97.00   $97.00  
  Purchase #2 $216.66   7.759%   $233.4706   $233.47   $233.45   $233.50  
  Purchase #3 $236.39   6.782%   $252.422   $252.42   $252.40   $252.40  
  Purchase #4 $241.45   6.751%   $257.7503   $257.75   $257.75   $257.80  
  Purchase #5 $181.37   11.794%   $202.7608   $202.76   $202.75   $202.80  
  Purchase #6 $250.82   7.597%   $269.8748   $269.87   $269.85   $269.90  
  Purchase #7 $83.70   8.609%   $90.9057   $90.91   $90.90   $90.90  
  7 purchase totals = $1,295.69       $1,404.1746   $1,404.17   $1,404.10   $1,404.30