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	$164.55	4.205%	$171.4693	$171.47	$171.45	$171.50
Purchase #2	$26.53	6.720%	$28.3128	$28.31	$28.30	$28.30
Purchase #3	$121.92	11.773%	$136.2736	$136.27	$136.25	$136.30
Purchase #4	$31.96	10.667%	$35.3692	$35.37	$35.35	$35.40
Purchase #5	$144.71	4.201%	$150.7893	$150.79	$150.80	$150.80
Purchase #6	$30.83	8.156%	$33.3445	$33.34	$33.35	$33.30
Purchase #7	$6.86	12.111%	$7.6908	$7.69	$7.70	$7.70
7 purchase totals =	$527.36		$563.2495	$563.24	$563.20	$563.30