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	$168.67	12.278%	$189.3793	$189.38	$189.40	$189.40
Purchase #2	$161.38	3.748%	$167.4285	$167.43	$167.45	$167.40
Purchase #3	$180.53	11.522%	$201.3307	$201.33	$201.35	$201.30
Purchase #4	$157.42	7.813%	$169.7192	$169.72	$169.70	$169.70
Purchase #5	$60.39	11.560%	$67.3711	$67.37	$67.35	$67.40
Purchase #6	$105.33	3.715%	$109.243	$109.24	$109.25	$109.20
Purchase #7	$99.72	3.689%	$103.3987	$103.40	$103.40	$103.40
7 purchase totals =	$933.44		$1,007.8705	$1,007.87	$1,007.90	$1,007.80