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 $200.34   12.212%   $224.8055   $224.81   $224.80   $224.80  
  Purchase #2 $97.51   12.112%   $109.3204   $109.32   $109.30   $109.30  
  Purchase #3 $216.99   9.191%   $236.9336   $236.93   $236.95   $236.90  
  Purchase #4 $43.25   5.181%   $45.4908   $45.49   $45.50   $45.50  
  Purchase #5 $31.37   6.803%   $33.5041   $33.50   $33.50   $33.50  
  Purchase #6 $183.30   12.447%   $206.1154   $206.12   $206.10   $206.10  
  Purchase #7 $240.93   9.258%   $263.2353   $263.24   $263.25   $263.20  
  7 purchase totals = $1,013.69       $1,119.4051   $1,119.41   $1,119.40   $1,119.30