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	$162.74	6.828%	$173.8519	$173.85	$173.85	$173.90
Purchase #2	$212.59	8.383%	$230.4114	$230.41	$230.40	$230.40
Purchase #3	$48.63	12.112%	$54.5201	$54.52	$54.50	$54.50
Purchase #4	$27.29	5.445%	$28.7759	$28.78	$28.80	$28.80
Purchase #5	$230.35	5.597%	$243.2427	$243.24	$243.25	$243.20
Purchase #6	$37.85	12.421%	$42.5513	$42.55	$42.55	$42.60
Purchase #7	$130.49	11.549%	$145.5603	$145.56	$145.55	$145.60
7 purchase totals =	$849.94		$918.9136	$918.91	$918.90	$919.00