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	$59.81	7.229%	$64.1337	$64.13	$64.15	$64.10
Purchase #2	$40.38	9.443%	$44.1931	$44.19	$44.20	$44.20
Purchase #3	$182.75	9.452%	$200.0235	$200.02	$200.00	$200.00
Purchase #4	$48.62	11.768%	$54.3416	$54.34	$54.35	$54.30
Purchase #5	$119.46	3.440%	$123.5694	$123.57	$123.55	$123.60
Purchase #6	$157.36	9.356%	$172.0826	$172.08	$172.10	$172.10
Purchase #7	$165.37	3.339%	$170.8917	$170.89	$170.90	$170.90
7 purchase totals =	$773.75		$829.2356	$829.22	$829.25	$829.20