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	$89.92	4.321%	$93.8054	$93.81	$93.80	$93.80
Purchase #2	$103.93	9.239%	$113.5321	$113.53	$113.55	$113.50
Purchase #3	$166.26	11.498%	$185.3766	$185.38	$185.40	$185.40
Purchase #4	$121.74	4.841%	$127.6334	$127.63	$127.65	$127.60
Purchase #5	$135.41	11.136%	$150.4893	$150.49	$150.50	$150.50
Purchase #6	$134.63	9.639%	$147.607	$147.61	$147.60	$147.60
Purchase #7	$34.84	7.657%	$37.5077	$37.51	$37.50	$37.50
7 purchase totals =	$786.73		$855.9515	$855.96	$856.00	$855.90