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	$75.48	13.481%	$85.6555	$85.66	$85.65	$85.70
Purchase #2	$239.58	10.355%	$264.3885	$264.39	$264.40	$264.40
Purchase #3	$72.85	10.537%	$80.5262	$80.53	$80.55	$80.50
Purchase #4	$52.73	8.228%	$57.0686	$57.07	$57.05	$57.10
Purchase #5	$130.46	3.126%	$134.5382	$134.54	$134.55	$134.50
Purchase #6	$99.50	11.612%	$111.0539	$111.05	$111.05	$111.10
Purchase #7	$158.25	8.578%	$171.8247	$171.82	$171.80	$171.80
7 purchase totals =	$828.85		$905.0556	$905.06	$905.05	$905.10