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	$240.57	10.816%	$266.5901	$266.59	$266.60	$266.60
Purchase #2	$55.92	9.429%	$61.1927	$61.19	$61.20	$61.20
Purchase #3	$122.42	12.353%	$137.5425	$137.54	$137.55	$137.50
Purchase #4	$60.48	11.789%	$67.61	$67.61	$67.60	$67.60
Purchase #5	$93.73	12.445%	$105.3947	$105.39	$105.40	$105.40
Purchase #6	$186.82	13.428%	$211.9062	$211.91	$211.90	$211.90
Purchase #7	$11.90	5.259%	$12.5258	$12.53	$12.55	$12.50
7 purchase totals =	$771.84		$862.7620	$862.76	$862.80	$862.70