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	$246.86	3.240%	$254.8583	$254.86	$254.85	$254.90
Purchase #2	$215.44	13.855%	$245.2892	$245.29	$245.30	$245.30
Purchase #3	$77.36	7.103%	$82.8549	$82.85	$82.85	$82.90
Purchase #4	$210.82	8.153%	$228.0082	$228.01	$228.00	$228.00
Purchase #5	$75.36	13.766%	$85.7341	$85.73	$85.75	$85.70
Purchase #6	$25.90	8.627%	$28.1344	$28.13	$28.15	$28.10
Purchase #7	$169.98	6.370%	$180.8077	$180.81	$180.80	$180.80
7 purchase totals =	$1,021.72		$1,105.6868	$1,105.68	$1,105.70	$1,105.70