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	$158.77	5.117%	$166.8943	$166.89	$166.90	$166.90
Purchase #2	$144.93	9.472%	$158.6578	$158.66	$158.65	$158.70
Purchase #3	$170.54	11.117%	$189.4989	$189.50	$189.50	$189.50
Purchase #4	$31.46	7.370%	$33.7786	$33.78	$33.80	$33.80
Purchase #5	$159.54	9.192%	$174.2049	$174.20	$174.20	$174.20
Purchase #6	$163.86	3.668%	$169.8704	$169.87	$169.85	$169.90
Purchase #7	$127.66	11.868%	$142.8107	$142.81	$142.80	$142.80
7 purchase totals =	$956.76		$1,035.7156	$1,035.71	$1,035.70	$1,035.80