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 $208.45   13.739%   $237.0889   $237.09   $237.10   $237.10  
  Purchase #2 $197.95   12.331%   $222.3592   $222.36   $222.35   $222.40  
  Purchase #3 $36.70   8.672%   $39.8826   $39.88   $39.90   $39.90  
  Purchase #4 $143.86   5.361%   $151.5723   $151.57   $151.55   $151.60  
  Purchase #5 $139.74   10.160%   $153.9376   $153.94   $153.95   $153.90  
  Purchase #6 $64.97   3.234%   $67.0711   $67.07   $67.05   $67.10  
  Purchase #7 $83.47   13.258%   $94.5365   $94.54   $94.55   $94.50  
  7 purchase totals = $875.14       $966.4482   $966.45   $966.45   $966.50