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	$79.60	11.224%	$88.5343	$88.53	$88.55	$88.50
Purchase #2	$73.72	13.371%	$83.5771	$83.58	$83.60	$83.60
Purchase #3	$19.88	8.768%	$21.6231	$21.62	$21.60	$21.60
Purchase #4	$39.82	3.498%	$41.2129	$41.21	$41.20	$41.20
Purchase #5	$98.40	12.439%	$110.64	$110.64	$110.65	$110.60
Purchase #6	$50.42	9.857%	$55.3899	$55.39	$55.40	$55.40
Purchase #7	$240.31	11.686%	$268.3926	$268.39	$268.40	$268.40
7 purchase totals =	$602.15		$669.3699	$669.36	$669.40	$669.30