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	$78.90	12.287%	$88.5944	$88.59	$88.60	$88.60
Purchase #2	$194.75	13.843%	$221.7092	$221.71	$221.70	$221.70
Purchase #3	$51.90	10.595%	$57.3988	$57.40	$57.40	$57.40
Purchase #4	$32.92	7.148%	$35.2731	$35.27	$35.25	$35.30
Purchase #5	$212.92	8.873%	$231.8124	$231.81	$231.80	$231.80
Purchase #6	$37.27	8.501%	$40.4383	$40.44	$40.45	$40.40
Purchase #7	$155.83	8.328%	$168.8075	$168.81	$168.80	$168.80
7 purchase totals =	$764.49		$844.0337	$844.03	$844.00	$844.00