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	$142.93	8.637%	$155.2749	$155.27	$155.25	$155.30
Purchase #2	$89.50	7.175%	$95.9216	$95.92	$95.90	$95.90
Purchase #3	$36.45	13.409%	$41.3376	$41.34	$41.35	$41.30
Purchase #4	$47.43	4.816%	$49.7142	$49.71	$49.70	$49.70
Purchase #5	$168.32	9.173%	$183.76	$183.76	$183.75	$183.80
Purchase #6	$130.64	12.777%	$147.3319	$147.33	$147.35	$147.30
Purchase #7	$116.88	5.569%	$123.389	$123.39	$123.40	$123.40
7 purchase totals =	$732.15		$796.7292	$796.72	$796.70	$796.70