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	$234.49	6.299%	$249.2605	$249.26	$249.25	$249.30
Purchase #2	$161.64	10.492%	$178.5993	$178.60	$178.60	$178.60
Purchase #3	$68.37	11.498%	$76.2312	$76.23	$76.25	$76.20
Purchase #4	$192.78	3.125%	$198.8044	$198.80	$198.80	$198.80
Purchase #5	$25.61	6.496%	$27.2736	$27.27	$27.25	$27.30
Purchase #6	$58.83	6.776%	$62.8163	$62.82	$62.80	$62.80
Purchase #7	$165.65	11.712%	$185.0509	$185.05	$185.05	$185.10
7 purchase totals =	$907.37		$978.0362	$978.03	$978.00	$978.10