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	$238.52	7.184%	$255.6553	$255.66	$255.65	$255.70
Purchase #2	$144.33	4.142%	$150.3081	$150.31	$150.30	$150.30
Purchase #3	$183.62	8.789%	$199.7584	$199.76	$199.75	$199.80
Purchase #4	$238.53	7.517%	$256.4603	$256.46	$256.45	$256.50
Purchase #5	$27.94	11.776%	$31.2302	$31.23	$31.25	$31.20
Purchase #6	$195.54	9.253%	$213.6333	$213.63	$213.65	$213.60
Purchase #7	$49.74	10.822%	$55.1229	$55.12	$55.10	$55.10
7 purchase totals =	$1,078.22		$1,162.1685	$1,162.17	$1,162.15	$1,162.20