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	$186.32	10.652%	$206.1668	$206.17	$206.15	$206.20
Purchase #2	$84.85	6.414%	$90.2923	$90.29	$90.30	$90.30
Purchase #3	$169.90	6.459%	$180.8738	$180.87	$180.85	$180.90
Purchase #4	$101.69	3.574%	$105.3244	$105.32	$105.30	$105.30
Purchase #5	$166.76	11.506%	$185.9474	$185.95	$185.95	$185.90
Purchase #6	$6.82	13.833%	$7.7634	$7.76	$7.75	$7.80
Purchase #7	$81.46	7.224%	$87.3447	$87.34	$87.35	$87.30
7 purchase totals =	$797.80		$863.7128	$863.70	$863.65	$863.70