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	$51.85	7.794%	$55.8912	$55.89	$55.90	$55.90
Purchase #2	$229.58	9.654%	$251.7437	$251.74	$251.75	$251.70
Purchase #3	$250.59	13.579%	$284.6176	$284.62	$284.60	$284.60
Purchase #4	$97.61	10.104%	$107.4725	$107.47	$107.45	$107.50
Purchase #5	$163.53	7.369%	$175.5805	$175.58	$175.60	$175.60
Purchase #6	$57.52	3.228%	$59.3767	$59.38	$59.40	$59.40
Purchase #7	$6.79	9.436%	$7.4307	$7.43	$7.45	$7.40
7 purchase totals =	$857.47		$942.1129	$942.11	$942.15	$942.10