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	$49.39	11.829%	$55.2323	$55.23	$55.25	$55.20
Purchase #2	$247.38	5.840%	$261.827	$261.83	$261.85	$261.80
Purchase #3	$22.50	11.352%	$25.0542	$25.05	$25.05	$25.10
Purchase #4	$123.34	10.360%	$136.118	$136.12	$136.10	$136.10
Purchase #5	$98.51	6.263%	$104.6797	$104.68	$104.70	$104.70
Purchase #6	$140.72	6.836%	$150.3396	$150.34	$150.35	$150.30
Purchase #7	$42.94	9.858%	$47.173	$47.17	$47.15	$47.20
7 purchase totals =	$724.78		$780.4238	$780.42	$780.45	$780.40