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	$200.90	10.583%	$222.1612	$222.16	$222.15	$222.20
Purchase #2	$133.64	8.226%	$144.6332	$144.63	$144.65	$144.60
Purchase #3	$83.36	3.472%	$86.2543	$86.25	$86.25	$86.30
Purchase #4	$72.35	13.484%	$82.1057	$82.11	$82.10	$82.10
Purchase #5	$210.62	6.194%	$223.6658	$223.67	$223.65	$223.70
Purchase #6	$83.29	7.277%	$89.351	$89.35	$89.35	$89.40
Purchase #7	$71.63	13.117%	$81.0257	$81.03	$81.05	$81.00
7 purchase totals =	$855.79		$929.1969	$929.20	$929.20	$929.30