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	$75.61	4.230%	$78.8083	$78.81	$78.80	$78.80
Purchase #2	$239.73	6.518%	$255.3556	$255.36	$255.35	$255.40
Purchase #3	$145.41	8.328%	$157.5197	$157.52	$157.50	$157.50
Purchase #4	$142.98	9.304%	$156.2829	$156.28	$156.30	$156.30
Purchase #5	$50.89	3.398%	$52.6192	$52.62	$52.60	$52.60
Purchase #6	$195.39	10.851%	$216.5918	$216.59	$216.60	$216.60
Purchase #7	$145.60	11.349%	$162.1241	$162.12	$162.10	$162.10
7 purchase totals =	$995.61		$1,079.3016	$1,079.30	$1,079.25	$1,079.30