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	$205.44	4.804%	$215.3093	$215.31	$215.30	$215.30
Purchase #2	$85.37	4.120%	$88.8872	$88.89	$88.90	$88.90
Purchase #3	$202.41	13.636%	$230.0106	$230.01	$230.00	$230.00
Purchase #4	$73.34	7.326%	$78.7129	$78.71	$78.70	$78.70
Purchase #5	$84.53	5.613%	$89.2747	$89.27	$89.25	$89.30
Purchase #6	$72.69	5.475%	$76.6698	$76.67	$76.65	$76.70
Purchase #7	$41.54	7.657%	$44.7207	$44.72	$44.70	$44.70
7 purchase totals =	$765.32		$823.5852	$823.58	$823.50	$823.60