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 $61.53   11.155%   $68.3937   $68.39   $68.40   $68.40  
  Purchase #2 $14.76   10.464%   $16.3045   $16.30   $16.30   $16.30  
  Purchase #3 $150.95   11.364%   $168.104   $168.10   $168.10   $168.10  
  Purchase #4 $73.87   10.111%   $81.339   $81.34   $81.35   $81.30  
  Purchase #5 $49.51   11.493%   $55.2002   $55.20   $55.20   $55.20  
  Purchase #6 $172.43   4.128%   $179.5479   $179.55   $179.55   $179.50  
  Purchase #7 $208.91   10.147%   $230.1081   $230.11   $230.10   $230.10  
  7 purchase totals = $731.96       $798.9974   $798.99   $799.00   $798.90