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 $63.44   10.405%   $70.0409   $70.04   $70.05   $70.00  
  Purchase #2 $162.49   6.864%   $173.6433   $173.64   $173.65   $173.60  
  Purchase #3 $64.45   4.183%   $67.1459   $67.15   $67.15   $67.10  
  Purchase #4 $157.39   5.272%   $165.6876   $165.69   $165.70   $165.70  
  Purchase #5 $219.82   3.232%   $226.9246   $226.92   $226.90   $226.90  
  Purchase #6 $136.36   4.481%   $142.4703   $142.47   $142.45   $142.50  
  Purchase #7 $206.40   8.182%   $223.2876   $223.29   $223.30   $223.30  
  7 purchase totals = $1,010.35       $1,069.2002   $1,069.20   $1,069.20   $1,069.10