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	$50.51	8.351%	$54.7281	$54.73	$54.75	$54.70
Purchase #2	$18.71	11.674%	$20.8942	$20.89	$20.90	$20.90
Purchase #3	$152.50	8.495%	$165.4549	$165.45	$165.45	$165.50
Purchase #4	$7.35	6.382%	$7.8191	$7.82	$7.80	$7.80
Purchase #5	$60.59	11.404%	$67.4997	$67.50	$67.50	$67.50
Purchase #6	$185.38	11.310%	$206.3465	$206.35	$206.35	$206.30
Purchase #7	$128.37	6.699%	$136.9695	$136.97	$136.95	$137.00
7 purchase totals =	$603.41		$659.7120	$659.71	$659.70	$659.70