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	$79.80	10.523%	$88.1974	$88.20	$88.20	$88.20
Purchase #2	$174.93	6.588%	$186.4544	$186.45	$186.45	$186.50
Purchase #3	$46.54	7.771%	$50.1566	$50.16	$50.15	$50.20
Purchase #4	$81.98	8.874%	$89.2549	$89.25	$89.25	$89.30
Purchase #5	$64.36	6.726%	$68.6889	$68.69	$68.70	$68.70
Purchase #6	$158.79	4.618%	$166.1229	$166.12	$166.10	$166.10
Purchase #7	$174.93	6.289%	$185.9313	$185.93	$185.95	$185.90
7 purchase totals =	$781.33		$834.8064	$834.80	$834.80	$834.90