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	$126.91	11.854%	$141.9539	$141.95	$141.95	$142.00
Purchase #2	$39.55	4.574%	$41.359	$41.36	$41.35	$41.40
Purchase #3	$27.72	13.773%	$31.5379	$31.54	$31.55	$31.50
Purchase #4	$193.62	10.811%	$214.5523	$214.55	$214.55	$214.60
Purchase #5	$44.56	13.475%	$50.5645	$50.56	$50.55	$50.60
Purchase #6	$89.31	3.197%	$92.1652	$92.17	$92.15	$92.20
Purchase #7	$33.29	11.566%	$37.1403	$37.14	$37.15	$37.10
7 purchase totals =	$554.96		$609.2731	$609.27	$609.25	$609.40