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	$95.87	4.773%	$100.4459	$100.45	$100.45	$100.40
Purchase #2	$230.73	12.750%	$260.1481	$260.15	$260.15	$260.10
Purchase #3	$89.42	8.540%	$97.0565	$97.06	$97.05	$97.10
Purchase #4	$24.59	3.423%	$25.4317	$25.43	$25.45	$25.40
Purchase #5	$143.86	8.732%	$156.4219	$156.42	$156.40	$156.40
Purchase #6	$73.39	4.550%	$76.7292	$76.73	$76.75	$76.70
Purchase #7	$71.31	9.614%	$78.1657	$78.17	$78.15	$78.20
7 purchase totals =	$729.17		$794.3990	$794.41	$794.40	$794.30