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 $182.44   10.601%   $201.7805   $201.78   $201.80   $201.80  
  Purchase #2 $90.49   6.691%   $96.5447   $96.54   $96.55   $96.50  
  Purchase #3 $98.54   11.214%   $109.5903   $109.59   $109.60   $109.60  
  Purchase #4 $140.36   4.770%   $147.0552   $147.06   $147.05   $147.10  
  Purchase #5 $13.55   3.560%   $14.0324   $14.03   $14.05   $14.00  
  Purchase #6 $215.33   11.833%   $240.81   $240.81   $240.80   $240.80  
  Purchase #7 $130.59   4.566%   $136.5527   $136.55   $136.55   $136.60  
  7 purchase totals = $871.30       $946.3658   $946.36   $946.40   $946.40