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 $108.30   10.454%   $119.6217   $119.62   $119.60   $119.60  
  Purchase #2 $56.66   6.529%   $60.3593   $60.36   $60.35   $60.40  
  Purchase #3 $12.29   7.824%   $13.2516   $13.25   $13.25   $13.30  
  Purchase #4 $139.82   10.794%   $154.9122   $154.91   $154.90   $154.90  
  Purchase #5 $147.39   3.106%   $151.9679   $151.97   $151.95   $152.00  
  Purchase #6 $222.66   13.191%   $252.0311   $252.03   $252.05   $252.00  
  Purchase #7 $238.64   13.390%   $270.5939   $270.59   $270.60   $270.60  
  7 purchase totals = $925.76       $1,022.7377   $1,022.73   $1,022.70   $1,022.80