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	$112.58	6.700%	$120.1229	$120.12	$120.10	$120.10
Purchase #2	$154.69	13.291%	$175.2498	$175.25	$175.25	$175.20
Purchase #3	$42.64	8.187%	$46.1309	$46.13	$46.15	$46.10
Purchase #4	$97.36	7.468%	$104.6308	$104.63	$104.65	$104.60
Purchase #5	$122.33	7.525%	$131.5353	$131.54	$131.55	$131.50
Purchase #6	$125.56	11.795%	$140.3698	$140.37	$140.35	$140.40
Purchase #7	$142.72	6.562%	$152.0853	$152.09	$152.10	$152.10
7 purchase totals =	$797.88		$870.1248	$870.13	$870.15	$870.00