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	$25.74	10.859%	$28.5351	$28.54	$28.55	$28.50
Purchase #2	$43.39	12.449%	$48.7916	$48.79	$48.80	$48.80
Purchase #3	$223.88	13.796%	$254.7665	$254.77	$254.75	$254.80
Purchase #4	$139.96	10.743%	$154.9959	$155.00	$155.00	$155.00
Purchase #5	$164.29	6.235%	$174.5335	$174.53	$174.55	$174.50
Purchase #6	$198.85	11.793%	$222.3004	$222.30	$222.30	$222.30
Purchase #7	$89.43	11.496%	$99.7109	$99.71	$99.70	$99.70
7 purchase totals =	$885.54		$983.6339	$983.64	$983.65	$983.60