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	$49.39	9.683%	$54.1724	$54.17	$54.15	$54.20
Purchase #2	$144.38	4.141%	$150.3588	$150.36	$150.35	$150.40
Purchase #3	$98.46	12.507%	$110.7744	$110.77	$110.75	$110.80
Purchase #4	$143.77	4.521%	$150.2698	$150.27	$150.25	$150.30
Purchase #5	$218.39	7.797%	$235.4179	$235.42	$235.40	$235.40
Purchase #6	$55.37	7.298%	$59.4109	$59.41	$59.40	$59.40
Purchase #7	$31.30	13.612%	$35.5606	$35.56	$35.55	$35.60
7 purchase totals =	$741.06		$795.9648	$795.96	$795.85	$796.10