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 $58.82   7.775%   $63.3933   $63.39   $63.40   $63.40  
  Purchase #2 $233.93   6.214%   $248.4664   $248.47   $248.45   $248.50  
  Purchase #3 $202.70   7.265%   $217.4262   $217.43   $217.45   $217.40  
  Purchase #4 $173.47   6.639%   $184.9867   $184.99   $185.00   $185.00  
  Purchase #5 $161.39   10.704%   $178.6652   $178.67   $178.65   $178.70  
  Purchase #6 $27.68   7.455%   $29.7435   $29.74   $29.75   $29.70  
  Purchase #7 $63.45   11.176%   $70.5412   $70.54   $70.55   $70.50  
  7 purchase totals = $921.44       $993.2225   $993.23   $993.25   $993.20