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 $9.42   5.802%   $9.9665   $9.97   $9.95   $10.00  
  Purchase #2 $7.44   8.621%   $8.0814   $8.08   $8.10   $8.10  
  Purchase #3 $173.67   3.130%   $179.1059   $179.11   $179.10   $179.10  
  Purchase #4 $158.54   9.810%   $174.0928   $174.09   $174.10   $174.10  
  Purchase #5 $75.29   6.622%   $80.2757   $80.28   $80.30   $80.30  
  Purchase #6 $217.85   13.267%   $246.7522   $246.75   $246.75   $246.80  
  Purchase #7 $186.70   10.599%   $206.4883   $206.49   $206.50   $206.50  
  7 purchase totals = $828.91       $904.7628   $904.77   $904.80   $904.90