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	$249.46	11.858%	$279.041	$279.04	$279.05	$279.00
Purchase #2	$152.50	9.148%	$166.4507	$166.45	$166.45	$166.50
Purchase #3	$243.58	8.306%	$263.8118	$263.81	$263.80	$263.80
Purchase #4	$53.62	6.596%	$57.1568	$57.16	$57.15	$57.20
Purchase #5	$171.30	9.155%	$186.9825	$186.98	$187.00	$187.00
Purchase #6	$79.41	12.172%	$89.0758	$89.08	$89.10	$89.10
Purchase #7	$128.93	3.446%	$133.3729	$133.37	$133.35	$133.40
7 purchase totals =	$1,078.80		$1,175.8915	$1,175.89	$1,175.90	$1,176.00