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	$53.57	5.116%	$56.3106	$56.31	$56.30	$56.30
Purchase #2	$72.94	8.162%	$78.8934	$78.89	$78.90	$78.90
Purchase #3	$175.96	11.682%	$196.5156	$196.52	$196.50	$196.50
Purchase #4	$174.99	5.212%	$184.1105	$184.11	$184.10	$184.10
Purchase #5	$238.83	6.834%	$255.1516	$255.15	$255.15	$255.20
Purchase #6	$43.76	11.519%	$48.8007	$48.80	$48.80	$48.80
Purchase #7	$135.50	11.837%	$151.5391	$151.54	$151.55	$151.50
7 purchase totals =	$895.55		$971.3215	$971.32	$971.30	$971.30