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	$118.32	10.687%	$130.9649	$130.96	$130.95	$131.00
Purchase #2	$171.60	9.804%	$188.4237	$188.42	$188.40	$188.40
Purchase #3	$152.93	9.786%	$167.8957	$167.90	$167.90	$167.90
Purchase #4	$89.85	10.232%	$99.0435	$99.04	$99.05	$99.00
Purchase #5	$14.57	12.741%	$16.4264	$16.43	$16.45	$16.40
Purchase #6	$181.51	3.458%	$187.7866	$187.79	$187.80	$187.80
Purchase #7	$76.94	6.464%	$81.9134	$81.91	$81.90	$81.90
7 purchase totals =	$805.72		$872.4542	$872.45	$872.45	$872.40