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	$177.69	6.116%	$188.5575	$188.56	$188.55	$188.60
Purchase #2	$172.61	10.758%	$191.1794	$191.18	$191.20	$191.20
Purchase #3	$79.45	12.152%	$89.1048	$89.10	$89.10	$89.10
Purchase #4	$96.46	5.658%	$101.9177	$101.92	$101.90	$101.90
Purchase #5	$119.95	11.137%	$133.3088	$133.31	$133.30	$133.30
Purchase #6	$29.64	12.445%	$33.3287	$33.33	$33.35	$33.30
Purchase #7	$133.96	13.696%	$152.3072	$152.31	$152.30	$152.30
7 purchase totals =	$809.76		$889.7041	$889.71	$889.70	$889.70