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	$115.56	12.399%	$129.8883	$129.89	$129.90	$129.90
Purchase #2	$155.45	11.217%	$172.8868	$172.89	$172.90	$172.90
Purchase #3	$55.94	10.654%	$61.8998	$61.90	$61.90	$61.90
Purchase #4	$214.56	3.606%	$222.297	$222.30	$222.30	$222.30
Purchase #5	$237.76	12.758%	$268.0934	$268.09	$268.10	$268.10
Purchase #6	$67.84	9.437%	$74.2421	$74.24	$74.25	$74.20
Purchase #7	$247.94	5.828%	$262.3899	$262.39	$262.40	$262.40
7 purchase totals =	$1,095.05		$1,191.6973	$1,191.70	$1,191.75	$1,191.70