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	$240.50	12.816%	$271.3225	$271.32	$271.30	$271.30
Purchase #2	$171.43	8.353%	$185.7495	$185.75	$185.75	$185.70
Purchase #3	$63.71	11.354%	$70.9436	$70.94	$70.95	$70.90
Purchase #4	$68.59	5.648%	$72.464	$72.46	$72.45	$72.50
Purchase #5	$151.79	12.607%	$170.9262	$170.93	$170.95	$170.90
Purchase #6	$81.56	4.175%	$84.9651	$84.97	$84.95	$85.00
Purchase #7	$136.54	5.869%	$144.5535	$144.55	$144.55	$144.60
7 purchase totals =	$914.12		$1,000.9244	$1,000.92	$1,000.90	$1,000.90