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 $24.83   3.271%   $25.6422   $25.64   $25.65   $25.60  
  Purchase #2 $120.70   12.117%   $135.3252   $135.33   $135.35   $135.30  
  Purchase #3 $185.69   4.839%   $194.6755   $194.68   $194.70   $194.70  
  Purchase #4 $5.57   12.675%   $6.276   $6.28   $6.30   $6.30  
  Purchase #5 $222.25   10.724%   $246.0841   $246.08   $246.10   $246.10  
  Purchase #6 $191.86   5.218%   $201.8713   $201.87   $201.85   $201.90  
  Purchase #7 $9.49   3.627%   $9.8342   $9.83   $9.85   $9.80  
  7 purchase totals = $760.39       $819.7085   $819.71   $819.80   $819.70