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	$43.74	11.377%	$48.7163	$48.72	$48.70	$48.70
Purchase #2	$183.87	8.417%	$199.3463	$199.35	$199.35	$199.30
Purchase #3	$132.56	5.291%	$139.5737	$139.57	$139.55	$139.60
Purchase #4	$85.97	4.185%	$89.5678	$89.57	$89.55	$89.60
Purchase #5	$138.77	6.562%	$147.8761	$147.88	$147.90	$147.90
Purchase #6	$58.36	5.357%	$61.4863	$61.49	$61.50	$61.50
Purchase #7	$40.64	3.832%	$42.1973	$42.20	$42.20	$42.20
7 purchase totals =	$683.91		$728.7638	$728.78	$728.75	$728.80