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	$99.63	6.837%	$106.4417	$106.44	$106.45	$106.40
Purchase #2	$25.49	10.849%	$28.2554	$28.26	$28.25	$28.30
Purchase #3	$35.31	11.681%	$39.4346	$39.43	$39.45	$39.40
Purchase #4	$69.78	3.763%	$72.4058	$72.41	$72.40	$72.40
Purchase #5	$103.78	13.832%	$118.1348	$118.13	$118.15	$118.10
Purchase #6	$45.46	10.591%	$50.2747	$50.27	$50.25	$50.30
Purchase #7	$7.58	5.729%	$8.0143	$8.01	$8.00	$8.00
7 purchase totals =	$387.03		$422.9613	$422.95	$422.95	$422.90