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	$48.43	6.487%	$51.5717	$51.57	$51.55	$51.60
Purchase #2	$87.31	9.432%	$95.5451	$95.55	$95.55	$95.50
Purchase #3	$204.31	9.528%	$223.7767	$223.78	$223.80	$223.80
Purchase #4	$34.81	8.241%	$37.6787	$37.68	$37.70	$37.70
Purchase #5	$89.42	9.711%	$98.1036	$98.10	$98.10	$98.10
Purchase #6	$36.32	8.104%	$39.2634	$39.26	$39.25	$39.30
Purchase #7	$45.71	13.394%	$51.8324	$51.83	$51.85	$51.80
7 purchase totals =	$546.31		$597.7716	$597.77	$597.80	$597.80