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	$70.69	13.317%	$80.1038	$80.10	$80.10	$80.10
Purchase #2	$89.69	10.479%	$99.0886	$99.09	$99.10	$99.10
Purchase #3	$158.54	9.778%	$174.042	$174.04	$174.05	$174.00
Purchase #4	$216.29	6.613%	$230.5933	$230.59	$230.60	$230.60
Purchase #5	$142.96	9.666%	$156.7785	$156.78	$156.80	$156.80
Purchase #6	$165.92	12.399%	$186.4924	$186.49	$186.50	$186.50
Purchase #7	$87.94	5.711%	$92.9623	$92.96	$92.95	$93.00
7 purchase totals =	$932.03		$1,020.0609	$1,020.05	$1,020.10	$1,020.10