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 $114.61   10.393%   $126.5214   $126.52   $126.50   $126.50  
  Purchase #2 $32.56   7.497%   $35.001   $35.00   $35.00   $35.00  
  Purchase #3 $248.45   6.853%   $265.4763   $265.48   $265.50   $265.50  
  Purchase #4 $89.45   10.409%   $98.7609   $98.76   $98.75   $98.80  
  Purchase #5 $147.40   6.537%   $157.0355   $157.04   $157.05   $157.00  
  Purchase #6 $50.41   4.509%   $52.683   $52.68   $52.70   $52.70  
  Purchase #7 $5.78   4.740%   $6.054   $6.05   $6.05   $6.10  
  7 purchase totals = $688.66       $741.5321   $741.53   $741.55   $741.60