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	$147.44	7.746%	$158.8607	$158.86	$158.85	$158.90
Purchase #2	$54.64	6.871%	$58.3943	$58.39	$58.40	$58.40
Purchase #3	$88.52	13.615%	$100.572	$100.57	$100.55	$100.60
Purchase #4	$196.82	7.751%	$212.0755	$212.08	$212.10	$212.10
Purchase #5	$78.79	3.369%	$81.4444	$81.44	$81.45	$81.40
Purchase #6	$205.56	8.627%	$223.2937	$223.29	$223.30	$223.30
Purchase #7	$83.84	12.491%	$94.3125	$94.31	$94.30	$94.30
7 purchase totals =	$855.61		$928.9531	$928.94	$928.95	$929.00