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	$123.34	6.599%	$131.4792	$131.48	$131.50	$131.50
Purchase #2	$111.27	11.120%	$123.6432	$123.64	$123.65	$123.60
Purchase #3	$182.30	4.799%	$191.0486	$191.05	$191.05	$191.00
Purchase #4	$17.63	6.534%	$18.7819	$18.78	$18.80	$18.80
Purchase #5	$44.25	7.495%	$47.5665	$47.57	$47.55	$47.60
Purchase #6	$114.33	4.315%	$119.2633	$119.26	$119.25	$119.30
Purchase #7	$26.40	13.865%	$30.0604	$30.06	$30.05	$30.10
7 purchase totals =	$619.52		$661.8431	$661.84	$661.85	$661.90