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	$35.39	6.633%	$37.7374	$37.74	$37.75	$37.70
Purchase #2	$81.90	12.162%	$91.8607	$91.86	$91.85	$91.90
Purchase #3	$97.35	5.849%	$103.044	$103.04	$103.05	$103.00
Purchase #4	$55.61	9.454%	$60.8674	$60.87	$60.85	$60.90
Purchase #5	$18.48	11.647%	$20.6324	$20.63	$20.65	$20.60
Purchase #6	$191.94	9.628%	$210.42	$210.42	$210.40	$210.40
Purchase #7	$56.93	13.165%	$64.4248	$64.42	$64.40	$64.40
7 purchase totals =	$537.60		$588.9867	$588.98	$588.95	$588.90