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	$101.66	12.485%	$114.3523	$114.35	$114.35	$114.40
Purchase #2	$36.35	13.426%	$41.2304	$41.23	$41.25	$41.20
Purchase #3	$35.95	4.720%	$37.6468	$37.65	$37.65	$37.60
Purchase #4	$129.43	9.151%	$141.2741	$141.27	$141.25	$141.30
Purchase #5	$38.38	12.399%	$43.1387	$43.14	$43.15	$43.10
Purchase #6	$36.34	12.294%	$40.8076	$40.81	$40.80	$40.80
Purchase #7	$185.49	8.334%	$200.9487	$200.95	$200.95	$200.90
7 purchase totals =	$563.60		$619.3986	$619.40	$619.40	$619.30