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	$48.32	5.864%	$51.1535	$51.15	$51.15	$51.20
Purchase #2	$113.34	9.799%	$124.4462	$124.45	$124.45	$124.40
Purchase #3	$210.61	13.391%	$238.8128	$238.81	$238.80	$238.80
Purchase #4	$85.70	5.566%	$90.4701	$90.47	$90.45	$90.50
Purchase #5	$13.84	9.769%	$15.192	$15.19	$15.20	$15.20
Purchase #6	$75.81	10.492%	$83.764	$83.76	$83.75	$83.80
Purchase #7	$27.27	7.399%	$29.2877	$29.29	$29.30	$29.30
7 purchase totals =	$574.89		$633.1263	$633.12	$633.10	$633.20