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	$78.31	13.772%	$89.0949	$89.09	$89.10	$89.10
Purchase #2	$121.79	10.287%	$134.3185	$134.32	$134.30	$134.30
Purchase #3	$142.66	13.557%	$162.0004	$162.00	$162.00	$162.00
Purchase #4	$54.30	10.424%	$59.9602	$59.96	$59.95	$60.00
Purchase #5	$83.33	9.774%	$91.4747	$91.47	$91.45	$91.50
Purchase #6	$23.56	12.374%	$26.4753	$26.48	$26.50	$26.50
Purchase #7	$118.75	9.694%	$130.2616	$130.26	$130.25	$130.30
7 purchase totals =	$622.70		$693.5856	$693.58	$693.55	$693.70