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	$53.36	4.487%	$55.7543	$55.75	$55.75	$55.80
Purchase #2	$136.77	6.824%	$146.1032	$146.10	$146.10	$146.10
Purchase #3	$173.31	5.485%	$182.8161	$182.82	$182.80	$182.80
Purchase #4	$103.44	4.711%	$108.3131	$108.31	$108.30	$108.30
Purchase #5	$80.96	10.357%	$89.345	$89.35	$89.35	$89.30
Purchase #6	$234.28	6.619%	$249.787	$249.79	$249.80	$249.80
Purchase #7	$12.64	4.190%	$13.1696	$13.17	$13.15	$13.20
7 purchase totals =	$794.76		$845.2883	$845.29	$845.25	$845.30