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	$191.74	9.695%	$210.3292	$210.33	$210.35	$210.30
Purchase #2	$229.64	11.479%	$256.0004	$256.00	$256.00	$256.00
Purchase #3	$134.79	4.508%	$140.8663	$140.87	$140.85	$140.90
Purchase #4	$118.73	10.596%	$131.3106	$131.31	$131.30	$131.30
Purchase #5	$136.96	6.466%	$145.8158	$145.82	$145.80	$145.80
Purchase #6	$39.82	10.171%	$43.8701	$43.87	$43.85	$43.90
Purchase #7	$7.61	13.702%	$8.6527	$8.65	$8.65	$8.70
7 purchase totals =	$859.29		$936.8451	$936.85	$936.80	$936.90