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	$71.29	13.632%	$81.0083	$81.01	$81.00	$81.00
Purchase #2	$171.56	10.385%	$189.3765	$189.38	$189.40	$189.40
Purchase #3	$123.86	10.435%	$136.7848	$136.78	$136.80	$136.80
Purchase #4	$93.35	7.598%	$100.4427	$100.44	$100.45	$100.40
Purchase #5	$34.86	11.682%	$38.9323	$38.93	$38.95	$38.90
Purchase #6	$133.67	6.716%	$142.6473	$142.65	$142.65	$142.60
Purchase #7	$53.29	3.473%	$55.1408	$55.14	$55.15	$55.10
7 purchase totals =	$681.88		$744.3327	$744.33	$744.40	$744.20