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	$114.93	7.479%	$123.5256	$123.53	$123.55	$123.50
Purchase #2	$157.87	5.663%	$166.8102	$166.81	$166.80	$166.80
Purchase #3	$101.82	3.612%	$105.4977	$105.50	$105.50	$105.50
Purchase #4	$167.82	9.221%	$183.2947	$183.29	$183.30	$183.30
Purchase #5	$197.33	11.718%	$220.4531	$220.45	$220.45	$220.50
Purchase #6	$57.53	9.291%	$62.8751	$62.88	$62.90	$62.90
Purchase #7	$110.79	7.722%	$119.3452	$119.35	$119.35	$119.30
7 purchase totals =	$908.09		$981.8016	$981.81	$981.85	$981.80