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 $162.76   13.466%   $184.6773   $184.68   $184.70   $184.70  
  Purchase #2 $99.71   5.362%   $105.0565   $105.06   $105.05   $105.10  
  Purchase #3 $17.77   7.488%   $19.1006   $19.10   $19.10   $19.10  
  Purchase #4 $187.57   10.640%   $207.5274   $207.53   $207.55   $207.50  
  Purchase #5 $229.33   7.381%   $246.2568   $246.26   $246.25   $246.30  
  Purchase #6 $11.27   12.649%   $12.6955   $12.70   $12.70   $12.70  
  Purchase #7 $53.74   9.599%   $58.8985   $58.90   $58.90   $58.90  
  7 purchase totals = $762.15       $834.2126   $834.23   $834.25   $834.30