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	$26.94	4.506%	$28.1539	$28.15	$28.15	$28.20
Purchase #2	$171.54	10.104%	$188.8724	$188.87	$188.85	$188.90
Purchase #3	$137.39	9.866%	$150.9449	$150.94	$150.95	$150.90
Purchase #4	$54.80	6.269%	$58.2354	$58.24	$58.25	$58.20
Purchase #5	$71.56	9.800%	$78.5729	$78.57	$78.55	$78.60
Purchase #6	$184.85	10.810%	$204.8323	$204.83	$204.85	$204.80
Purchase #7	$67.36	5.867%	$71.312	$71.31	$71.30	$71.30
7 purchase totals =	$714.44		$780.9238	$780.91	$780.90	$780.90