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 $49.96   13.292%   $56.6007   $56.60   $56.60   $56.60  
  Purchase #2 $21.53   7.237%   $23.0881   $23.09   $23.10   $23.10  
  Purchase #3 $97.30   3.737%   $100.9361   $100.94   $100.95   $100.90  
  Purchase #4 $71.64   6.794%   $76.5072   $76.51   $76.50   $76.50  
  Purchase #5 $65.95   3.291%   $68.1204   $68.12   $68.10   $68.10  
  Purchase #6 $244.60   7.249%   $262.3311   $262.33   $262.35   $262.30  
  Purchase #7 $173.62   4.450%   $181.3461   $181.35   $181.35   $181.30  
  7 purchase totals = $724.60       $768.9297   $768.94   $768.95   $768.80