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	$85.80	6.154%	$91.0801	$91.08	$91.10	$91.10
Purchase #2	$53.89	8.858%	$58.6636	$58.66	$58.65	$58.70
Purchase #3	$81.42	10.354%	$89.8502	$89.85	$89.85	$89.90
Purchase #4	$86.31	6.358%	$91.7976	$91.80	$91.80	$91.80
Purchase #5	$90.49	5.742%	$95.6859	$95.69	$95.70	$95.70
Purchase #6	$169.34	7.674%	$182.3352	$182.34	$182.35	$182.30
Purchase #7	$166.57	3.680%	$172.6998	$172.70	$172.70	$172.70
7 purchase totals =	$733.82		$782.1124	$782.12	$782.15	$782.20