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	$54.41	9.707%	$59.6916	$59.69	$59.70	$59.70
Purchase #2	$53.25	8.266%	$57.6516	$57.65	$57.65	$57.70
Purchase #3	$20.61	10.814%	$22.8388	$22.84	$22.85	$22.80
Purchase #4	$152.86	11.502%	$170.442	$170.44	$170.45	$170.40
Purchase #5	$233.29	13.320%	$264.3642	$264.36	$264.35	$264.40
Purchase #6	$125.31	4.276%	$130.6683	$130.67	$130.65	$130.70
Purchase #7	$37.36	13.102%	$42.2549	$42.25	$42.25	$42.30
7 purchase totals =	$677.09		$747.9114	$747.90	$747.90	$748.00