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	$142.78	9.178%	$155.8843	$155.88	$155.90	$155.90
Purchase #2	$87.59	8.474%	$95.0124	$95.01	$95.00	$95.00
Purchase #3	$80.37	9.334%	$87.8717	$87.87	$87.85	$87.90
Purchase #4	$52.52	4.293%	$54.7747	$54.77	$54.75	$54.80
Purchase #5	$183.58	4.153%	$191.2041	$191.20	$191.20	$191.20
Purchase #6	$228.59	6.439%	$243.3089	$243.31	$243.30	$243.30
Purchase #7	$215.29	3.251%	$222.2891	$222.29	$222.30	$222.30
7 purchase totals =	$990.72		$1,050.3452	$1,050.33	$1,050.30	$1,050.40