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 $52.88   10.726%   $58.5519   $58.55   $58.55   $58.60  
  Purchase #2 $33.77   3.300%   $34.8844   $34.88   $34.90   $34.90  
  Purchase #3 $166.70   10.719%   $184.5686   $184.57   $184.55   $184.60  
  Purchase #4 $63.47   5.726%   $67.1043   $67.10   $67.10   $67.10  
  Purchase #5 $92.74   3.621%   $96.0981   $96.10   $96.10   $96.10  
  Purchase #6 $60.61   7.368%   $65.0757   $65.08   $65.10   $65.10  
  Purchase #7 $243.28   5.713%   $257.1786   $257.18   $257.20   $257.20  
  7 purchase totals = $713.45       $763.4616   $763.46   $763.50   $763.60