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	$113.60	12.791%	$128.1306	$128.13	$128.15	$128.10
Purchase #2	$83.95	9.373%	$91.8186	$91.82	$91.80	$91.80
Purchase #3	$50.68	7.317%	$54.3883	$54.39	$54.40	$54.40
Purchase #4	$97.41	6.152%	$103.4027	$103.40	$103.40	$103.40
Purchase #5	$247.61	6.740%	$264.2989	$264.30	$264.30	$264.30
Purchase #6	$104.67	5.797%	$110.7377	$110.74	$110.75	$110.70
Purchase #7	$244.60	8.673%	$265.8142	$265.81	$265.80	$265.80
7 purchase totals =	$942.52		$1,018.5910	$1,018.59	$1,018.60	$1,018.50