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 $109.28   6.556%   $116.4444   $116.44   $116.45   $116.40  
  Purchase #2 $194.89   6.147%   $206.8699   $206.87   $206.85   $206.90  
  Purchase #3 $72.54   13.547%   $82.367   $82.37   $82.35   $82.40  
  Purchase #4 $21.81   12.320%   $24.497   $24.50   $24.50   $24.50  
  Purchase #5 $214.80   10.319%   $236.9652   $236.97   $236.95   $237.00  
  Purchase #6 $240.85   4.754%   $252.3   $252.30   $252.30   $252.30  
  Purchase #7 $49.41   5.254%   $52.006   $52.01   $52.00   $52.00  
  7 purchase totals = $903.58       $971.4495   $971.46   $971.40   $971.50