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	$88.28	12.299%	$99.1376	$99.14	$99.15	$99.10
Purchase #2	$7.82	6.357%	$8.3171	$8.32	$8.30	$8.30
Purchase #3	$62.39	9.707%	$68.4462	$68.45	$68.45	$68.40
Purchase #4	$125.40	3.123%	$129.3162	$129.32	$129.30	$129.30
Purchase #5	$38.86	12.273%	$43.6293	$43.63	$43.65	$43.60
Purchase #6	$76.30	9.752%	$83.7408	$83.74	$83.75	$83.70
Purchase #7	$66.43	9.293%	$72.6033	$72.60	$72.60	$72.60
7 purchase totals =	$465.48		$505.1905	$505.20	$505.20	$505.00