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	$129.69	10.588%	$143.4216	$143.42	$143.40	$143.40
Purchase #2	$27.83	3.438%	$28.7868	$28.79	$28.80	$28.80
Purchase #3	$91.40	5.846%	$96.7432	$96.74	$96.75	$96.70
Purchase #4	$155.90	5.493%	$164.4636	$164.46	$164.45	$164.50
Purchase #5	$127.54	9.372%	$139.493	$139.49	$139.50	$139.50
Purchase #6	$39.58	8.214%	$42.8311	$42.83	$42.85	$42.80
Purchase #7	$30.72	9.216%	$33.5512	$33.55	$33.55	$33.60
7 purchase totals =	$602.66		$649.2905	$649.28	$649.30	$649.30