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	$143.99	10.710%	$159.4113	$159.41	$159.40	$159.40
Purchase #2	$42.38	12.632%	$47.7334	$47.73	$47.75	$47.70
Purchase #3	$85.56	12.225%	$96.0197	$96.02	$96.00	$96.00
Purchase #4	$172.50	13.873%	$196.4309	$196.43	$196.45	$196.40
Purchase #5	$64.94	11.683%	$72.5269	$72.53	$72.55	$72.50
Purchase #6	$162.53	12.500%	$182.8463	$182.85	$182.85	$182.80
Purchase #7	$207.64	9.295%	$226.9401	$226.94	$226.95	$226.90
7 purchase totals =	$879.54		$981.9086	$981.91	$981.95	$981.70