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 $228.99   6.259%   $243.3225   $243.32   $243.30   $243.30  
  Purchase #2 $55.89   5.376%   $58.8946   $58.89   $58.90   $58.90  
  Purchase #3 $163.72   8.435%   $177.5298   $177.53   $177.55   $177.50  
  Purchase #4 $191.74   13.542%   $217.7054   $217.71   $217.70   $217.70  
  Purchase #5 $150.39   11.851%   $168.2127   $168.21   $168.20   $168.20  
  Purchase #6 $136.42   7.154%   $146.1795   $146.18   $146.20   $146.20  
  Purchase #7 $84.72   7.197%   $90.8173   $90.82   $90.80   $90.80  
  7 purchase totals = $1,011.87       $1,102.6618   $1,102.66   $1,102.65   $1,102.60