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 $187.87   4.669%   $196.6417   $196.64   $196.65   $196.60  
  Purchase #2 $229.87   13.588%   $261.1047   $261.10   $261.10   $261.10  
  Purchase #3 $158.95   11.830%   $177.7538   $177.75   $177.75   $177.80  
  Purchase #4 $216.29   3.773%   $224.4506   $224.45   $224.45   $224.50  
  Purchase #5 $57.32   6.554%   $61.0768   $61.08   $61.10   $61.10  
  Purchase #6 $50.46   12.280%   $56.6565   $56.66   $56.65   $56.70  
  Purchase #7 $10.47   13.170%   $11.8489   $11.85   $11.85   $11.80  
  7 purchase totals = $911.23       $989.5330   $989.53   $989.55   $989.60