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	$40.42	4.537%	$42.2539	$42.25	$42.25	$42.30
Purchase #2	$84.82	5.813%	$89.7506	$89.75	$89.75	$89.80
Purchase #3	$62.43	8.150%	$67.518	$67.52	$67.50	$67.50
Purchase #4	$216.92	5.165%	$228.1239	$228.12	$228.10	$228.10
Purchase #5	$168.62	11.799%	$188.5155	$188.52	$188.50	$188.50
Purchase #6	$245.73	4.171%	$255.9794	$255.98	$256.00	$256.00
Purchase #7	$45.49	3.105%	$46.9025	$46.90	$46.90	$46.90
7 purchase totals =	$864.43		$919.0438	$919.04	$919.00	$919.10