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	$73.40	6.492%	$78.1651	$78.17	$78.15	$78.20
Purchase #2	$61.58	5.308%	$64.8487	$64.85	$64.85	$64.80
Purchase #3	$237.87	6.441%	$253.1912	$253.19	$253.20	$253.20
Purchase #4	$188.79	4.228%	$196.772	$196.77	$196.75	$196.80
Purchase #5	$73.60	7.685%	$79.2562	$79.26	$79.25	$79.30
Purchase #6	$245.27	6.164%	$260.3884	$260.39	$260.40	$260.40
Purchase #7	$224.89	12.764%	$253.595	$253.60	$253.60	$253.60
7 purchase totals =	$1,105.40		$1,186.2166	$1,186.23	$1,186.20	$1,186.30