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	$51.56	10.109%	$56.7722	$56.77	$56.75	$56.80
Purchase #2	$100.68	11.801%	$112.5612	$112.56	$112.55	$112.60
Purchase #3	$194.26	3.572%	$201.199	$201.20	$201.20	$201.20
Purchase #4	$179.45	11.787%	$200.6018	$200.60	$200.60	$200.60
Purchase #5	$179.46	3.267%	$185.323	$185.32	$185.30	$185.30
Purchase #6	$91.26	12.623%	$102.7797	$102.78	$102.80	$102.80
Purchase #7	$59.52	13.592%	$67.61	$67.61	$67.60	$67.60
7 purchase totals =	$856.19		$926.8469	$926.84	$926.80	$926.90