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	$67.89	9.441%	$74.2995	$74.30	$74.30	$74.30
Purchase #2	$234.78	9.831%	$257.8612	$257.86	$257.85	$257.90
Purchase #3	$54.91	7.621%	$59.0947	$59.09	$59.10	$59.10
Purchase #4	$234.98	12.483%	$264.3126	$264.31	$264.30	$264.30
Purchase #5	$151.83	5.798%	$160.6331	$160.63	$160.65	$160.60
Purchase #6	$89.30	3.177%	$92.1371	$92.14	$92.15	$92.10
Purchase #7	$108.96	7.712%	$117.363	$117.36	$117.35	$117.40
7 purchase totals =	$942.65		$1,025.7012	$1,025.69	$1,025.70	$1,025.70