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	$135.54	4.642%	$141.8318	$141.83	$141.85	$141.80
Purchase #2	$191.57	10.566%	$211.8113	$211.81	$211.80	$211.80
Purchase #3	$201.80	10.333%	$222.652	$222.65	$222.65	$222.70
Purchase #4	$197.34	12.421%	$221.8516	$221.85	$221.85	$221.90
Purchase #5	$227.42	10.162%	$250.5304	$250.53	$250.55	$250.50
Purchase #6	$90.45	10.708%	$100.1354	$100.14	$100.15	$100.10
Purchase #7	$157.39	9.370%	$172.1374	$172.14	$172.15	$172.10
7 purchase totals =	$1,201.51		$1,320.9499	$1,320.95	$1,321.00	$1,320.90