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 $67.49   6.442%   $71.8377   $71.84   $71.85   $71.80  
  Purchase #2 $144.83   3.311%   $149.6253   $149.63   $149.65   $149.60  
  Purchase #3 $203.72   5.779%   $215.493   $215.49   $215.50   $215.50  
  Purchase #4 $206.50   3.628%   $213.9918   $213.99   $214.00   $214.00  
  Purchase #5 $220.61   8.111%   $238.5037   $238.50   $238.50   $238.50  
  Purchase #6 $190.41   10.856%   $211.0809   $211.08   $211.10   $211.10  
  Purchase #7 $154.48   12.646%   $174.0155   $174.02   $174.00   $174.00  
  7 purchase totals = $1,188.04       $1,274.5479   $1,274.55   $1,274.60   $1,274.50