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 $86.87   11.137%   $96.5447   $96.54   $96.55   $96.50  
  Purchase #2 $100.26   6.691%   $106.9684   $106.97   $106.95   $107.00  
  Purchase #3 $120.45   9.840%   $132.3023   $132.30   $132.30   $132.30  
  Purchase #4 $26.87   12.692%   $30.2803   $30.28   $30.30   $30.30  
  Purchase #5 $154.69   10.447%   $170.8505   $170.85   $170.85   $170.90  
  Purchase #6 $200.73   8.754%   $218.3019   $218.30   $218.30   $218.30  
  Purchase #7 $32.72   8.225%   $35.4112   $35.41   $35.40   $35.40  
  7 purchase totals = $722.59       $790.6593   $790.65   $790.65   $790.70