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	$37.75	11.323%	$42.0244	$42.02	$42.00	$42.00
Purchase #2	$166.88	7.711%	$179.7481	$179.75	$179.75	$179.70
Purchase #3	$159.99	7.534%	$172.0436	$172.04	$172.05	$172.00
Purchase #4	$65.54	4.600%	$68.5548	$68.55	$68.55	$68.60
Purchase #5	$91.98	9.572%	$100.7843	$100.78	$100.80	$100.80
Purchase #6	$164.68	9.238%	$179.8931	$179.89	$179.90	$179.90
Purchase #7	$97.45	7.257%	$104.5219	$104.52	$104.50	$104.50
7 purchase totals =	$784.27		$847.5702	$847.55	$847.55	$847.50