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	$137.62	13.610%	$156.3501	$156.35	$156.35	$156.40
Purchase #2	$118.64	3.160%	$122.389	$122.39	$122.40	$122.40
Purchase #3	$57.29	4.465%	$59.848	$59.85	$59.85	$59.80
Purchase #4	$89.61	13.790%	$101.9672	$101.97	$101.95	$102.00
Purchase #5	$98.61	5.399%	$103.934	$103.93	$103.95	$103.90
Purchase #6	$182.32	5.160%	$191.7277	$191.73	$191.75	$191.70
Purchase #7	$228.96	6.712%	$244.3278	$244.33	$244.35	$244.30
7 purchase totals =	$913.05		$980.5438	$980.55	$980.60	$980.50