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	$110.65	11.216%	$123.0605	$123.06	$123.05	$123.10
Purchase #2	$59.31	10.129%	$65.3175	$65.32	$65.30	$65.30
Purchase #3	$64.71	12.557%	$72.8356	$72.84	$72.85	$72.80
Purchase #4	$7.80	13.616%	$8.862	$8.86	$8.85	$8.90
Purchase #5	$56.97	3.695%	$59.075	$59.08	$59.10	$59.10
Purchase #6	$74.41	7.440%	$79.9461	$79.95	$79.95	$79.90
Purchase #7	$230.66	13.374%	$261.5085	$261.51	$261.50	$261.50
7 purchase totals =	$604.51		$670.6052	$670.62	$670.60	$670.60