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	$92.75	6.762%	$99.0218	$99.02	$99.00	$99.00
Purchase #2	$41.75	3.754%	$43.3173	$43.32	$43.30	$43.30
Purchase #3	$39.64	8.157%	$42.8734	$42.87	$42.85	$42.90
Purchase #4	$237.90	4.375%	$248.3081	$248.31	$248.30	$248.30
Purchase #5	$95.76	8.865%	$104.2491	$104.25	$104.25	$104.20
Purchase #6	$178.49	7.755%	$192.3319	$192.33	$192.35	$192.30
Purchase #7	$99.45	12.744%	$112.1239	$112.12	$112.10	$112.10
7 purchase totals =	$785.74		$842.2255	$842.22	$842.15	$842.10