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 $151.59   9.506%   $166.0001   $166.00   $166.00   $166.00  
  Purchase #2 $195.65   11.370%   $217.8954   $217.90   $217.90   $217.90  
  Purchase #3 $147.76   6.193%   $156.9108   $156.91   $156.90   $156.90  
  Purchase #4 $144.50   9.537%   $158.281   $158.28   $158.30   $158.30  
  Purchase #5 $168.56   6.163%   $178.9484   $178.95   $178.95   $178.90  
  Purchase #6 $232.70   8.725%   $253.0031   $253.00   $253.00   $253.00  
  Purchase #7 $52.44   8.563%   $56.9304   $56.93   $56.95   $56.90  
  7 purchase totals = $1,093.20       $1,187.9692   $1,187.97   $1,188.00   $1,187.90