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	$48.80	4.605%	$51.0472	$51.05	$51.05	$51.00
Purchase #2	$83.38	5.685%	$88.1202	$88.12	$88.10	$88.10
Purchase #3	$152.95	12.870%	$172.6347	$172.63	$172.65	$172.60
Purchase #4	$161.49	6.174%	$171.4604	$171.46	$171.45	$171.50
Purchase #5	$28.42	12.121%	$31.8648	$31.86	$31.85	$31.90
Purchase #6	$165.32	13.339%	$187.372	$187.37	$187.35	$187.40
Purchase #7	$13.90	8.229%	$15.0438	$15.04	$15.05	$15.00
7 purchase totals =	$654.26		$717.5431	$717.53	$717.50	$717.50