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	$108.98	10.415%	$120.3303	$120.33	$120.35	$120.30
Purchase #2	$90.48	5.411%	$95.3759	$95.38	$95.40	$95.40
Purchase #3	$124.82	5.178%	$131.2832	$131.28	$131.30	$131.30
Purchase #4	$193.36	6.501%	$205.9303	$205.93	$205.95	$205.90
Purchase #5	$39.72	9.658%	$43.5562	$43.56	$43.55	$43.60
Purchase #6	$99.68	5.394%	$105.0567	$105.06	$105.05	$105.10
Purchase #7	$67.70	12.627%	$76.2485	$76.25	$76.25	$76.20
7 purchase totals =	$724.74		$777.7811	$777.79	$777.85	$777.80