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	$131.54	4.494%	$137.4514	$137.45	$137.45	$137.50
Purchase #2	$242.70	3.346%	$250.8207	$250.82	$250.80	$250.80
Purchase #3	$238.27	12.654%	$268.4207	$268.42	$268.40	$268.40
Purchase #4	$85.59	10.256%	$94.3681	$94.37	$94.35	$94.40
Purchase #5	$222.81	9.573%	$244.1396	$244.14	$244.15	$244.10
Purchase #6	$13.55	11.663%	$15.1303	$15.13	$15.15	$15.10
Purchase #7	$68.72	9.466%	$75.225	$75.23	$75.25	$75.20
7 purchase totals =	$1,003.18		$1,085.5558	$1,085.56	$1,085.55	$1,085.50