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	$39.46	3.175%	$40.7129	$40.71	$40.70	$40.70
Purchase #2	$77.69	6.714%	$82.9061	$82.91	$82.90	$82.90
Purchase #3	$152.74	11.593%	$170.4471	$170.45	$170.45	$170.40
Purchase #4	$165.65	6.535%	$176.4752	$176.48	$176.50	$176.50
Purchase #5	$67.64	7.301%	$72.5784	$72.58	$72.60	$72.60
Purchase #6	$26.67	4.159%	$27.7792	$27.78	$27.80	$27.80
Purchase #7	$242.31	3.368%	$250.471	$250.47	$250.45	$250.50
7 purchase totals =	$772.16		$821.3699	$821.38	$821.40	$821.40