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	$140.72	7.550%	$151.3444	$151.34	$151.35	$151.30
Purchase #2	$34.58	5.389%	$36.4435	$36.44	$36.45	$36.40
Purchase #3	$119.97	13.573%	$136.2535	$136.25	$136.25	$136.30
Purchase #4	$7.56	13.134%	$8.5529	$8.55	$8.55	$8.60
Purchase #5	$250.86	9.242%	$274.0445	$274.04	$274.05	$274.00
Purchase #6	$73.41	12.372%	$82.4923	$82.49	$82.50	$82.50
Purchase #7	$159.40	13.459%	$180.8536	$180.85	$180.85	$180.90
7 purchase totals =	$786.50		$869.9847	$869.96	$870.00	$870.00