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	$168.51	12.170%	$189.0177	$189.02	$189.00	$189.00
Purchase #2	$32.48	13.189%	$36.7638	$36.76	$36.75	$36.80
Purchase #3	$127.88	5.375%	$134.7536	$134.75	$134.75	$134.80
Purchase #4	$172.94	9.674%	$189.6702	$189.67	$189.65	$189.70
Purchase #5	$85.96	4.188%	$89.56	$89.56	$89.55	$89.60
Purchase #6	$181.77	5.551%	$191.8601	$191.86	$191.85	$191.90
Purchase #7	$131.35	7.552%	$141.2696	$141.27	$141.25	$141.30
7 purchase totals =	$900.89		$972.8950	$972.89	$972.80	$973.10