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 $96.84   4.554%   $101.2501   $101.25   $101.25   $101.30  
  Purchase #2 $61.37   5.178%   $64.5477   $64.55   $64.55   $64.50  
  Purchase #3 $216.36   6.737%   $230.9362   $230.94   $230.95   $230.90  
  Purchase #4 $105.40   4.827%   $110.4877   $110.49   $110.50   $110.50  
  Purchase #5 $201.61   9.866%   $221.5008   $221.50   $221.50   $221.50  
  Purchase #6 $102.94   4.403%   $107.4724   $107.47   $107.45   $107.50  
  Purchase #7 $177.54   7.380%   $190.6425   $190.64   $190.65   $190.60  
  7 purchase totals = $962.06       $1,026.8374   $1,026.84   $1,026.85   $1,026.80