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	$35.82	10.814%	$39.6936	$39.69	$39.70	$39.70
Purchase #2	$228.79	5.842%	$242.1559	$242.16	$242.15	$242.20
Purchase #3	$138.29	9.292%	$151.1399	$151.14	$151.15	$151.10
Purchase #4	$39.89	9.192%	$43.5567	$43.56	$43.55	$43.60
Purchase #5	$204.93	6.563%	$218.3796	$218.38	$218.40	$218.40
Purchase #6	$66.33	8.258%	$71.8075	$71.81	$71.80	$71.80
Purchase #7	$118.47	8.807%	$128.9037	$128.90	$128.90	$128.90
7 purchase totals =	$832.52		$895.6369	$895.64	$895.65	$895.70