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	$43.31	4.147%	$45.1061	$45.11	$45.10	$45.10
Purchase #2	$120.37	7.400%	$129.2774	$129.28	$129.30	$129.30
Purchase #3	$7.79	7.239%	$8.3539	$8.35	$8.35	$8.40
Purchase #4	$229.30	11.435%	$255.5205	$255.52	$255.50	$255.50
Purchase #5	$43.69	8.394%	$47.3573	$47.36	$47.35	$47.40
Purchase #6	$18.52	8.603%	$20.1133	$20.11	$20.10	$20.10
Purchase #7	$28.35	5.443%	$29.8931	$29.89	$29.90	$29.90
7 purchase totals =	$491.33		$535.6216	$535.62	$535.60	$535.70