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	$18.28	10.374%	$20.1764	$20.18	$20.20	$20.20
Purchase #2	$96.58	8.634%	$104.9187	$104.92	$104.90	$104.90
Purchase #3	$121.84	12.560%	$137.1431	$137.14	$137.15	$137.10
Purchase #4	$189.35	10.186%	$208.6372	$208.64	$208.65	$208.60
Purchase #5	$181.67	8.139%	$196.4561	$196.46	$196.45	$196.50
Purchase #6	$19.56	9.110%	$21.3419	$21.34	$21.35	$21.30
Purchase #7	$51.88	10.567%	$57.3622	$57.36	$57.35	$57.40
7 purchase totals =	$679.16		$746.0356	$746.04	$746.05	$746.00