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 $156.37   6.168%   $166.0149   $166.01   $166.00   $166.00  
  Purchase #2 $156.50   6.408%   $166.5285   $166.53   $166.55   $166.50  
  Purchase #3 $27.45   11.614%   $30.638   $30.64   $30.65   $30.60  
  Purchase #4 $61.49   9.209%   $67.1526   $67.15   $67.15   $67.20  
  Purchase #5 $246.90   6.131%   $262.0374   $262.04   $262.05   $262.00  
  Purchase #6 $51.25   9.668%   $56.2049   $56.20   $56.20   $56.20  
  Purchase #7 $118.41   6.625%   $126.2547   $126.25   $126.25   $126.30  
  7 purchase totals = $818.37       $874.8310   $874.82   $874.85   $874.80