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 $63.90   9.412%   $69.9143   $69.91   $69.90   $69.90  
  Purchase #2 $207.86   8.634%   $225.8066   $225.81   $225.80   $225.80  
  Purchase #3 $111.44   7.170%   $119.4302   $119.43   $119.45   $119.40  
  Purchase #4 $68.58   11.203%   $76.263   $76.26   $76.25   $76.30  
  Purchase #5 $41.65   7.774%   $44.8879   $44.89   $44.90   $44.90  
  Purchase #6 $153.94   6.207%   $163.4951   $163.50   $163.50   $163.50  
  Purchase #7 $65.70   7.629%   $70.7123   $70.71   $70.70   $70.70  
  7 purchase totals = $713.07       $770.5094   $770.51   $770.50   $770.50