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	$55.34	7.671%	$59.5851	$59.59	$59.60	$59.60
Purchase #2	$227.79	11.772%	$254.6054	$254.61	$254.60	$254.60
Purchase #3	$39.36	6.313%	$41.8448	$41.84	$41.85	$41.80
Purchase #4	$95.44	7.716%	$102.8042	$102.80	$102.80	$102.80
Purchase #5	$128.86	5.746%	$136.2643	$136.26	$136.25	$136.30
Purchase #6	$175.45	11.497%	$195.6215	$195.62	$195.60	$195.60
Purchase #7	$122.52	7.612%	$131.8462	$131.85	$131.85	$131.80
7 purchase totals =	$844.76		$922.5715	$922.57	$922.55	$922.50