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	$168.80	6.340%	$179.5019	$179.50	$179.50	$179.50
Purchase #2	$246.39	12.721%	$277.7333	$277.73	$277.75	$277.70
Purchase #3	$77.40	3.135%	$79.8265	$79.83	$79.85	$79.80
Purchase #4	$65.86	11.435%	$73.3911	$73.39	$73.40	$73.40
Purchase #5	$125.88	4.256%	$131.2375	$131.24	$131.25	$131.20
Purchase #6	$228.85	12.171%	$256.7033	$256.70	$256.70	$256.70
Purchase #7	$157.35	4.506%	$164.4402	$164.44	$164.45	$164.40
7 purchase totals =	$1,070.53		$1,162.8338	$1,162.83	$1,162.90	$1,162.70