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	$164.81	7.220%	$176.7093	$176.71	$176.70	$176.70
Purchase #2	$77.89	13.372%	$88.3055	$88.31	$88.30	$88.30
Purchase #3	$142.52	6.454%	$151.7182	$151.72	$151.70	$151.70
Purchase #4	$47.89	10.192%	$52.7709	$52.77	$52.75	$52.80
Purchase #5	$82.52	8.673%	$89.677	$89.68	$89.70	$89.70
Purchase #6	$235.75	6.334%	$250.6824	$250.68	$250.70	$250.70
Purchase #7	$73.59	6.104%	$78.0819	$78.08	$78.10	$78.10
7 purchase totals =	$824.97		$887.9452	$887.95	$887.95	$888.00