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 $188.55   4.265%   $196.5917   $196.59   $196.60   $196.60  
  Purchase #2 $193.37   13.508%   $219.4904   $219.49   $219.50   $219.50  
  Purchase #3 $32.81   11.676%   $36.6409   $36.64   $36.65   $36.60  
  Purchase #4 $236.51   12.568%   $266.2346   $266.23   $266.25   $266.20  
  Purchase #5 $84.34   10.720%   $93.3812   $93.38   $93.40   $93.40  
  Purchase #6 $183.34   3.210%   $189.2252   $189.23   $189.25   $189.20  
  Purchase #7 $44.72   7.412%   $48.0346   $48.03   $48.05   $48.00  
  7 purchase totals = $963.64       $1,049.5986   $1,049.59   $1,049.70   $1,049.50