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	$45.94	11.716%	$51.3223	$51.32	$51.30	$51.30
Purchase #2	$32.51	10.399%	$35.8907	$35.89	$35.90	$35.90
Purchase #3	$100.96	5.174%	$106.1837	$106.18	$106.20	$106.20
Purchase #4	$238.78	13.630%	$271.3257	$271.33	$271.35	$271.30
Purchase #5	$67.47	12.660%	$76.0117	$76.01	$76.00	$76.00
Purchase #6	$196.52	13.218%	$222.496	$222.50	$222.50	$222.50
Purchase #7	$29.27	3.760%	$30.3706	$30.37	$30.35	$30.40
7 purchase totals =	$711.45		$793.6007	$793.60	$793.60	$793.60