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	$39.93	5.838%	$42.2611	$42.26	$42.25	$42.30
Purchase #2	$141.36	6.428%	$150.4466	$150.45	$150.45	$150.40
Purchase #3	$199.98	9.229%	$218.4362	$218.44	$218.45	$218.40
Purchase #4	$185.25	5.196%	$194.8756	$194.88	$194.90	$194.90
Purchase #5	$54.35	9.188%	$59.3437	$59.34	$59.35	$59.30
Purchase #6	$31.43	8.565%	$34.122	$34.12	$34.10	$34.10
Purchase #7	$118.63	3.708%	$123.0288	$123.03	$123.05	$123.00
7 purchase totals =	$770.93		$822.5140	$822.52	$822.55	$822.40