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	$250.51	7.190%	$268.5217	$268.52	$268.50	$268.50
Purchase #2	$85.59	5.128%	$89.9791	$89.98	$90.00	$90.00
Purchase #3	$28.42	13.124%	$32.1498	$32.15	$32.15	$32.10
Purchase #4	$98.69	8.250%	$106.8319	$106.83	$106.85	$106.80
Purchase #5	$224.99	3.119%	$232.0074	$232.01	$232.00	$232.00
Purchase #6	$212.91	7.717%	$229.3403	$229.34	$229.35	$229.30
Purchase #7	$169.37	7.797%	$182.5758	$182.58	$182.60	$182.60
7 purchase totals =	$1,070.48		$1,141.4060	$1,141.41	$1,141.45	$1,141.30