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	$47.63	7.802%	$51.3461	$51.35	$51.35	$51.30
Purchase #2	$89.71	9.794%	$98.4962	$98.50	$98.50	$98.50
Purchase #3	$224.91	12.613%	$253.2779	$253.28	$253.30	$253.30
Purchase #4	$158.75	7.810%	$171.1484	$171.15	$171.15	$171.10
Purchase #5	$113.59	11.673%	$126.8494	$126.85	$126.85	$126.80
Purchase #6	$129.95	13.723%	$147.783	$147.78	$147.80	$147.80
Purchase #7	$168.93	13.454%	$191.6578	$191.66	$191.65	$191.70
7 purchase totals =	$933.47		$1,040.5588	$1,040.57	$1,040.60	$1,040.50