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 $56.28   5.360%   $59.2966   $59.30   $59.30   $59.30  
  Purchase #2 $222.29   8.510%   $241.2069   $241.21   $241.20   $241.20  
  Purchase #3 $41.69   12.624%   $46.9529   $46.95   $46.95   $47.00  
  Purchase #4 $195.42   4.411%   $204.04   $204.04   $204.05   $204.00  
  Purchase #5 $208.95   7.851%   $225.3547   $225.35   $225.35   $225.40  
  Purchase #6 $53.46   12.857%   $60.3334   $60.33   $60.35   $60.30  
  Purchase #7 $16.82   13.146%   $19.0312   $19.03   $19.05   $19.00  
  7 purchase totals = $794.91       $856.2157   $856.21   $856.25   $856.20