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	$89.89	8.326%	$97.3742	$97.37	$97.35	$97.40
Purchase #2	$230.56	7.331%	$247.4624	$247.46	$247.45	$247.50
Purchase #3	$97.48	12.282%	$109.4525	$109.45	$109.45	$109.50
Purchase #4	$42.61	9.475%	$46.6473	$46.65	$46.65	$46.60
Purchase #5	$119.75	10.512%	$132.3381	$132.34	$132.35	$132.30
Purchase #6	$223.45	6.744%	$238.5195	$238.52	$238.50	$238.50
Purchase #7	$61.38	12.267%	$68.9095	$68.91	$68.90	$68.90
7 purchase totals =	$865.12		$940.7035	$940.70	$940.65	$940.70