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	$55.81	13.375%	$63.2746	$63.27	$63.25	$63.30
Purchase #2	$208.90	5.137%	$219.6312	$219.63	$219.65	$219.60
Purchase #3	$73.74	8.328%	$79.8811	$79.88	$79.90	$79.90
Purchase #4	$239.31	6.573%	$255.0398	$255.04	$255.05	$255.00
Purchase #5	$145.34	13.619%	$165.1339	$165.13	$165.15	$165.10
Purchase #6	$48.80	13.179%	$55.2314	$55.23	$55.25	$55.20
Purchase #7	$222.61	12.821%	$251.1508	$251.15	$251.15	$251.20
7 purchase totals =	$994.51		$1,089.3428	$1,089.33	$1,089.40	$1,089.30