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	$72.81	12.415%	$81.8494	$81.85	$81.85	$81.80
Purchase #2	$54.90	6.799%	$58.6327	$58.63	$58.65	$58.60
Purchase #3	$79.98	12.300%	$89.8175	$89.82	$89.80	$89.80
Purchase #4	$149.72	10.248%	$165.0633	$165.06	$165.05	$165.10
Purchase #5	$26.36	4.666%	$27.59	$27.59	$27.60	$27.60
Purchase #6	$35.29	9.868%	$38.7724	$38.77	$38.75	$38.80
Purchase #7	$133.51	4.322%	$139.2803	$139.28	$139.30	$139.30
7 purchase totals =	$552.57		$601.0056	$601.00	$601.00	$601.00