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	$54.35	4.112%	$56.5849	$56.58	$56.60	$56.60
Purchase #2	$39.38	7.399%	$42.2937	$42.29	$42.30	$42.30
Purchase #3	$223.87	8.724%	$243.4004	$243.40	$243.40	$243.40
Purchase #4	$235.83	12.827%	$266.0799	$266.08	$266.10	$266.10
Purchase #5	$31.34	12.873%	$35.3744	$35.37	$35.35	$35.40
Purchase #6	$176.39	13.732%	$200.6119	$200.61	$200.60	$200.60
Purchase #7	$178.61	6.779%	$190.718	$190.72	$190.70	$190.70
7 purchase totals =	$939.77		$1,035.0632	$1,035.05	$1,035.05	$1,035.10