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 $196.37   5.839%   $207.836   $207.84   $207.85   $207.80  
  Purchase #2 $82.27   4.153%   $85.6867   $85.69   $85.70   $85.70  
  Purchase #3 $48.64   13.780%   $55.3426   $55.34   $55.35   $55.30  
  Purchase #4 $109.79   5.585%   $115.9218   $115.92   $115.90   $115.90  
  Purchase #5 $219.91   8.776%   $239.2093   $239.21   $239.20   $239.20  
  Purchase #6 $74.31   9.348%   $81.2565   $81.26   $81.25   $81.30  
  Purchase #7 $178.67   6.586%   $190.4372   $190.44   $190.45   $190.40  
  7 purchase totals = $909.96       $975.6901   $975.70   $975.70   $975.60