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	$167.88	12.654%	$189.1235	$189.12	$189.10	$189.10
Purchase #2	$113.96	4.188%	$118.7326	$118.73	$118.75	$118.70
Purchase #3	$105.70	8.637%	$114.8293	$114.83	$114.85	$114.80
Purchase #4	$58.54	4.212%	$61.0057	$61.01	$61.00	$61.00
Purchase #5	$164.77	4.495%	$172.1764	$172.18	$172.20	$172.20
Purchase #6	$120.39	9.357%	$131.6549	$131.65	$131.65	$131.70
Purchase #7	$35.55	4.256%	$37.063	$37.06	$37.05	$37.10
7 purchase totals =	$766.79		$824.5854	$824.58	$824.60	$824.60