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	$32.42	12.690%	$36.5341	$36.53	$36.55	$36.50
Purchase #2	$234.60	12.789%	$264.603	$264.60	$264.60	$264.60
Purchase #3	$33.96	8.549%	$36.8632	$36.86	$36.85	$36.90
Purchase #4	$104.78	11.426%	$116.7522	$116.75	$116.75	$116.80
Purchase #5	$242.86	3.201%	$250.6339	$250.63	$250.65	$250.60
Purchase #6	$153.78	13.700%	$174.8479	$174.85	$174.85	$174.80
Purchase #7	$174.97	7.717%	$188.4724	$188.47	$188.45	$188.50
7 purchase totals =	$977.37		$1,068.7067	$1,068.69	$1,068.70	$1,068.70