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	$157.46	9.758%	$172.8249	$172.82	$172.80	$172.80
Purchase #2	$82.63	10.228%	$91.0814	$91.08	$91.10	$91.10
Purchase #3	$88.26	9.589%	$96.7233	$96.72	$96.70	$96.70
Purchase #4	$223.75	3.512%	$231.6081	$231.61	$231.60	$231.60
Purchase #5	$127.33	7.518%	$136.9027	$136.90	$136.90	$136.90
Purchase #6	$116.38	9.836%	$127.8271	$127.83	$127.85	$127.80
Purchase #7	$52.86	3.843%	$54.8914	$54.89	$54.90	$54.90
7 purchase totals =	$848.67		$911.8589	$911.85	$911.85	$911.80