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 $129.94   8.790%   $141.3617   $141.36   $141.35   $141.40  
  Purchase #2 $202.73   4.106%   $211.0541   $211.05   $211.05   $211.10  
  Purchase #3 $237.92   4.334%   $248.2315   $248.23   $248.25   $248.20  
  Purchase #4 $160.51   10.650%   $177.6043   $177.60   $177.60   $177.60  
  Purchase #5 $214.57   9.302%   $234.5293   $234.53   $234.55   $234.50  
  Purchase #6 $87.63   9.809%   $96.2256   $96.23   $96.25   $96.20  
  Purchase #7 $227.61   8.390%   $246.7065   $246.71   $246.70   $246.70  
  7 purchase totals = $1,260.91       $1,355.7130   $1,355.71   $1,355.75   $1,355.70