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 $126.61   7.477%   $136.0766   $136.08   $136.10   $136.10  
  Purchase #2 $46.67   11.536%   $52.0539   $52.05   $52.05   $52.10  
  Purchase #3 $22.99   8.304%   $24.8991   $24.90   $24.90   $24.90  
  Purchase #4 $248.50   8.522%   $269.6772   $269.68   $269.70   $269.70  
  Purchase #5 $40.99   12.841%   $46.2535   $46.25   $46.25   $46.30  
  Purchase #6 $200.93   9.556%   $220.1309   $220.13   $220.15   $220.10  
  Purchase #7 $22.60   6.691%   $24.1122   $24.11   $24.10   $24.10  
  7 purchase totals = $709.29       $773.2034   $773.20   $773.25   $773.30