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	$199.83	11.739%	$223.288	$223.29	$223.30	$223.30
Purchase #2	$146.98	12.301%	$165.06	$165.06	$165.05	$165.10
Purchase #3	$34.25	12.788%	$38.6299	$38.63	$38.65	$38.60
Purchase #4	$67.38	4.226%	$70.2275	$70.23	$70.25	$70.20
Purchase #5	$29.91	7.692%	$32.2107	$32.21	$32.20	$32.20
Purchase #6	$114.97	3.470%	$118.9595	$118.96	$118.95	$119.00
Purchase #7	$80.98	12.304%	$90.9438	$90.94	$90.95	$90.90
7 purchase totals =	$674.30		$739.3194	$739.32	$739.35	$739.30