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	$65.50	4.470%	$68.4279	$68.43	$68.45	$68.40
Purchase #2	$238.94	12.562%	$268.9556	$268.96	$268.95	$269.00
Purchase #3	$131.78	4.137%	$137.2317	$137.23	$137.25	$137.20
Purchase #4	$156.68	3.813%	$162.6542	$162.65	$162.65	$162.70
Purchase #5	$98.30	7.317%	$105.4926	$105.49	$105.50	$105.50
Purchase #6	$98.87	13.688%	$112.4033	$112.40	$112.40	$112.40
Purchase #7	$105.31	12.734%	$118.7202	$118.72	$118.70	$118.70
7 purchase totals =	$895.38		$973.8855	$973.88	$973.90	$973.90