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	$135.40	5.586%	$142.9634	$142.96	$142.95	$143.00
Purchase #2	$84.64	4.165%	$88.1653	$88.17	$88.15	$88.20
Purchase #3	$201.55	12.861%	$227.4713	$227.47	$227.45	$227.50
Purchase #4	$165.41	3.608%	$171.378	$171.38	$171.40	$171.40
Purchase #5	$159.87	3.196%	$164.9794	$164.98	$165.00	$165.00
Purchase #6	$130.35	10.737%	$144.3457	$144.35	$144.35	$144.30
Purchase #7	$35.42	9.609%	$38.8235	$38.82	$38.80	$38.80
7 purchase totals =	$912.64		$978.1266	$978.13	$978.10	$978.20