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 $225.44   8.386%   $244.3454   $244.35   $244.35   $244.30  
  Purchase #2 $101.61   7.611%   $109.3435   $109.34   $109.35   $109.30  
  Purchase #3 $209.44   6.330%   $222.6976   $222.70   $222.70   $222.70  
  Purchase #4 $185.74   5.181%   $195.3632   $195.36   $195.35   $195.40  
  Purchase #5 $26.93   12.371%   $30.2615   $30.26   $30.25   $30.30  
  Purchase #6 $179.45   12.826%   $202.4663   $202.47   $202.45   $202.50  
  Purchase #7 $50.44   8.653%   $54.8046   $54.80   $54.80   $54.80  
  7 purchase totals = $979.05       $1,059.2821   $1,059.28   $1,059.25   $1,059.30