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	$14.55	7.125%	$15.5867	$15.59	$15.60	$15.60
Purchase #2	$218.28	3.735%	$226.4328	$226.43	$226.45	$226.40
Purchase #3	$243.51	8.594%	$264.4372	$264.44	$264.45	$264.40
Purchase #4	$80.80	10.494%	$89.2792	$89.28	$89.30	$89.30
Purchase #5	$53.65	11.318%	$59.7221	$59.72	$59.70	$59.70
Purchase #6	$193.57	8.693%	$210.397	$210.40	$210.40	$210.40
Purchase #7	$25.70	6.259%	$27.3086	$27.31	$27.30	$27.30
7 purchase totals =	$830.06		$893.1636	$893.17	$893.20	$893.10