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	$43.92	7.404%	$47.1718	$47.17	$47.15	$47.20
Purchase #2	$96.26	10.678%	$106.5386	$106.54	$106.55	$106.50
Purchase #3	$93.47	7.218%	$100.2167	$100.22	$100.20	$100.20
Purchase #4	$40.98	3.339%	$42.3483	$42.35	$42.35	$42.30
Purchase #5	$36.42	10.399%	$40.2073	$40.21	$40.20	$40.20
Purchase #6	$30.43	13.820%	$34.6354	$34.64	$34.65	$34.60
Purchase #7	$236.41	5.162%	$248.6135	$248.61	$248.60	$248.60
7 purchase totals =	$577.89		$619.7316	$619.74	$619.70	$619.60