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	$217.47	9.523%	$238.1797	$238.18	$238.20	$238.20
Purchase #2	$149.86	12.375%	$168.4052	$168.41	$168.40	$168.40
Purchase #3	$225.83	4.314%	$235.5723	$235.57	$235.55	$235.60
Purchase #4	$232.56	6.399%	$247.4415	$247.44	$247.45	$247.40
Purchase #5	$170.59	8.668%	$185.3767	$185.38	$185.40	$185.40
Purchase #6	$66.48	13.663%	$75.5632	$75.56	$75.55	$75.60
Purchase #7	$54.61	9.292%	$59.6844	$59.68	$59.70	$59.70
7 purchase totals =	$1,117.40		$1,210.2230	$1,210.22	$1,210.25	$1,210.30