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	$243.82	12.849%	$275.1484	$275.15	$275.15	$275.10
Purchase #2	$82.50	8.548%	$89.5521	$89.55	$89.55	$89.60
Purchase #3	$153.25	9.319%	$167.5314	$167.53	$167.55	$167.50
Purchase #4	$124.98	5.193%	$131.4702	$131.47	$131.45	$131.50
Purchase #5	$223.27	8.561%	$242.3841	$242.38	$242.40	$242.40
Purchase #6	$200.70	3.505%	$207.7345	$207.73	$207.75	$207.70
Purchase #7	$180.60	10.705%	$199.9332	$199.93	$199.95	$199.90
7 purchase totals =	$1,209.12		$1,313.7539	$1,313.74	$1,313.80	$1,313.70