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	$83.64	7.776%	$90.1438	$90.14	$90.15	$90.10
Purchase #2	$39.25	7.487%	$42.1886	$42.19	$42.20	$42.20
Purchase #3	$64.65	11.821%	$72.2923	$72.29	$72.30	$72.30
Purchase #4	$126.81	5.835%	$134.2094	$134.21	$134.20	$134.20
Purchase #5	$193.42	3.545%	$200.2767	$200.28	$200.30	$200.30
Purchase #6	$204.27	10.128%	$224.9585	$224.96	$224.95	$225.00
Purchase #7	$146.34	3.334%	$151.219	$151.22	$151.20	$151.20
7 purchase totals =	$858.38		$915.2883	$915.29	$915.30	$915.30