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	$149.92	11.212%	$166.729	$166.73	$166.75	$166.70
Purchase #2	$233.69	3.780%	$242.5235	$242.52	$242.50	$242.50
Purchase #3	$7.48	3.333%	$7.7293	$7.73	$7.75	$7.70
Purchase #4	$91.92	12.466%	$103.3787	$103.38	$103.40	$103.40
Purchase #5	$97.36	3.129%	$100.4064	$100.41	$100.40	$100.40
Purchase #6	$145.53	11.851%	$162.7768	$162.78	$162.80	$162.80
Purchase #7	$26.49	3.225%	$27.3443	$27.34	$27.35	$27.30
7 purchase totals =	$752.39		$810.8880	$810.89	$810.95	$810.80