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 $44.84   11.416%   $49.9589   $49.96   $49.95   $50.00  
  Purchase #2 $97.48   9.109%   $106.3595   $106.36   $106.35   $106.40  
  Purchase #3 $23.83   10.458%   $26.3221   $26.32   $26.30   $26.30  
  Purchase #4 $52.40   5.329%   $55.1924   $55.19   $55.20   $55.20  
  Purchase #5 $27.64   13.711%   $31.4297   $31.43   $31.45   $31.40  
  Purchase #6 $176.37   4.613%   $184.5059   $184.51   $184.50   $184.50  
  Purchase #7 $163.90   5.557%   $173.0079   $173.01   $173.00   $173.00  
  7 purchase totals = $586.46       $626.7764   $626.78   $626.75   $626.80