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	$172.39	6.633%	$183.8246	$183.82	$183.80	$183.80
Purchase #2	$108.25	11.609%	$120.8167	$120.82	$120.80	$120.80
Purchase #3	$114.53	11.580%	$127.7926	$127.79	$127.80	$127.80
Purchase #4	$220.28	11.377%	$245.3413	$245.34	$245.35	$245.30
Purchase #5	$161.97	5.668%	$171.1505	$171.15	$171.15	$171.20
Purchase #6	$82.65	9.432%	$90.4455	$90.45	$90.45	$90.40
Purchase #7	$97.34	11.808%	$108.8339	$108.83	$108.85	$108.80
7 purchase totals =	$957.41		$1,048.2051	$1,048.20	$1,048.20	$1,048.10