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	$39.99	7.667%	$43.056	$43.06	$43.05	$43.10
Purchase #2	$159.59	3.421%	$165.0496	$165.05	$165.05	$165.00
Purchase #3	$196.76	6.814%	$210.1672	$210.17	$210.15	$210.20
Purchase #4	$144.98	10.647%	$160.416	$160.42	$160.40	$160.40
Purchase #5	$100.71	8.362%	$109.1314	$109.13	$109.15	$109.10
Purchase #6	$22.66	12.806%	$25.5618	$25.56	$25.55	$25.60
Purchase #7	$101.89	10.291%	$112.3755	$112.38	$112.40	$112.40
7 purchase totals =	$766.58		$825.7575	$825.77	$825.75	$825.80