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	$127.38	12.370%	$143.1369	$143.14	$143.15	$143.10
Purchase #2	$248.75	3.258%	$256.8543	$256.85	$256.85	$256.90
Purchase #3	$107.54	12.284%	$120.7502	$120.75	$120.75	$120.80
Purchase #4	$147.35	13.281%	$166.9196	$166.92	$166.90	$166.90
Purchase #5	$119.89	3.671%	$124.2912	$124.29	$124.30	$124.30
Purchase #6	$151.33	7.359%	$162.4664	$162.47	$162.45	$162.50
Purchase #7	$208.43	4.289%	$217.3696	$217.37	$217.35	$217.40
7 purchase totals =	$1,110.67		$1,191.7882	$1,191.79	$1,191.75	$1,191.90