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	$126.45	9.292%	$138.1997	$138.20	$138.20	$138.20
Purchase #2	$89.41	10.842%	$99.1038	$99.10	$99.10	$99.10
Purchase #3	$46.36	12.653%	$52.2259	$52.23	$52.25	$52.20
Purchase #4	$69.31	3.108%	$71.4642	$71.46	$71.45	$71.50
Purchase #5	$38.74	5.660%	$40.9327	$40.93	$40.95	$40.90
Purchase #6	$167.45	5.283%	$176.2964	$176.30	$176.30	$176.30
Purchase #7	$244.43	12.670%	$275.3993	$275.40	$275.40	$275.40
7 purchase totals =	$782.15		$853.6220	$853.62	$853.65	$853.60