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 $8.90   11.810%   $9.9511   $9.95   $9.95   $10.00  
  Purchase #2 $8.41   9.466%   $9.2061   $9.21   $9.20   $9.20  
  Purchase #3 $83.60   4.555%   $87.408   $87.41   $87.40   $87.40  
  Purchase #4 $228.91   4.492%   $239.1926   $239.19   $239.20   $239.20  
  Purchase #5 $39.70   13.459%   $45.0432   $45.04   $45.05   $45.00  
  Purchase #6 $90.41   7.254%   $96.9683   $96.97   $96.95   $97.00  
  Purchase #7 $40.77   10.810%   $45.1772   $45.18   $45.20   $45.20  
  7 purchase totals = $500.70       $532.9465   $532.95   $532.95   $533.00