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	$32.71	13.830%	$37.2338	$37.23	$37.25	$37.20
Purchase #2	$240.68	10.233%	$265.3088	$265.31	$265.30	$265.30
Purchase #3	$148.42	5.799%	$157.0269	$157.03	$157.05	$157.00
Purchase #4	$86.56	3.782%	$89.8337	$89.83	$89.85	$89.80
Purchase #5	$50.58	3.128%	$52.1621	$52.16	$52.15	$52.20
Purchase #6	$218.51	6.805%	$233.3796	$233.38	$233.40	$233.40
Purchase #7	$64.79	10.217%	$71.4096	$71.41	$71.40	$71.40
7 purchase totals =	$842.25		$906.3545	$906.35	$906.40	$906.30