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	$103.53	11.830%	$115.7776	$115.78	$115.80	$115.80
Purchase #2	$243.49	11.720%	$272.027	$272.03	$272.05	$272.00
Purchase #3	$220.29	9.192%	$240.5391	$240.54	$240.55	$240.50
Purchase #4	$237.45	11.796%	$265.4596	$265.46	$265.45	$265.50
Purchase #5	$147.33	6.268%	$156.5646	$156.56	$156.55	$156.60
Purchase #6	$30.71	4.657%	$32.1402	$32.14	$32.15	$32.10
Purchase #7	$85.45	5.227%	$89.9165	$89.92	$89.90	$89.90
7 purchase totals =	$1,068.25		$1,172.4246	$1,172.43	$1,172.45	$1,172.40