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	$37.89	11.317%	$42.178	$42.18	$42.20	$42.20
Purchase #2	$73.80	10.621%	$81.6383	$81.64	$81.65	$81.60
Purchase #3	$78.58	13.342%	$89.0641	$89.06	$89.05	$89.10
Purchase #4	$225.53	12.105%	$252.8304	$252.83	$252.85	$252.80
Purchase #5	$147.25	12.538%	$165.7122	$165.71	$165.70	$165.70
Purchase #6	$96.84	6.357%	$102.9961	$103.00	$103.00	$103.00
Purchase #7	$42.89	5.611%	$45.2966	$45.30	$45.30	$45.30
7 purchase totals =	$702.78		$779.7157	$779.72	$779.75	$779.70