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 $143.97   5.578%   $152.0006   $152.00   $152.00   $152.00  
  Purchase #2 $44.83   4.337%   $46.7743   $46.77   $46.75   $46.80  
  Purchase #3 $65.31   9.229%   $71.3375   $71.34   $71.35   $71.30  
  Purchase #4 $171.86   12.834%   $193.9165   $193.92   $193.90   $193.90  
  Purchase #5 $208.79   4.169%   $217.4945   $217.49   $217.50   $217.50  
  Purchase #6 $199.27   9.451%   $218.103   $218.10   $218.10   $218.10  
  Purchase #7 $50.27   6.695%   $53.6356   $53.64   $53.65   $53.60  
  7 purchase totals = $884.30       $953.2620   $953.26   $953.25   $953.20