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	$128.29	12.122%	$143.8413	$143.84	$143.85	$143.80
Purchase #2	$113.49	5.796%	$120.0679	$120.07	$120.05	$120.10
Purchase #3	$152.35	10.196%	$167.8836	$167.88	$167.90	$167.90
Purchase #4	$164.40	6.459%	$175.0186	$175.02	$175.00	$175.00
Purchase #5	$249.72	9.753%	$274.0752	$274.08	$274.10	$274.10
Purchase #6	$209.57	7.438%	$225.1578	$225.16	$225.15	$225.20
Purchase #7	$52.78	6.621%	$56.2746	$56.27	$56.25	$56.30
7 purchase totals =	$1,070.60		$1,162.3190	$1,162.32	$1,162.30	$1,162.40