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	$36.98	7.423%	$39.725	$39.73	$39.75	$39.70
Purchase #2	$196.28	10.314%	$216.5243	$216.52	$216.50	$216.50
Purchase #3	$105.51	6.408%	$112.2711	$112.27	$112.25	$112.30
Purchase #4	$116.45	6.329%	$123.8201	$123.82	$123.80	$123.80
Purchase #5	$127.32	10.194%	$140.299	$140.30	$140.30	$140.30
Purchase #6	$147.65	11.292%	$164.3226	$164.32	$164.30	$164.30
Purchase #7	$56.94	6.663%	$60.7339	$60.73	$60.75	$60.70
7 purchase totals =	$787.13		$857.6960	$857.69	$857.65	$857.60