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 $185.41   12.808%   $209.1573   $209.16   $209.15   $209.20  
  Purchase #2 $171.96   10.744%   $190.4354   $190.44   $190.45   $190.40  
  Purchase #3 $86.25   10.484%   $95.2925   $95.29   $95.30   $95.30  
  Purchase #4 $179.32   8.714%   $194.9459   $194.95   $194.95   $194.90  
  Purchase #5 $247.28   7.519%   $265.873   $265.87   $265.85   $265.90  
  Purchase #6 $177.32   4.165%   $184.7054   $184.71   $184.70   $184.70  
  Purchase #7 $24.55   11.183%   $27.2954   $27.30   $27.30   $27.30  
  7 purchase totals = $1,072.09       $1,167.7049   $1,167.72   $1,167.70   $1,167.70