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	$147.81	12.157%	$165.7793	$165.78	$165.80	$165.80
Purchase #2	$16.37	10.394%	$18.0715	$18.07	$18.05	$18.10
Purchase #3	$166.93	11.374%	$185.9166	$185.92	$185.90	$185.90
Purchase #4	$58.38	9.856%	$64.1339	$64.13	$64.15	$64.10
Purchase #5	$73.63	8.298%	$79.7398	$79.74	$79.75	$79.70
Purchase #6	$78.96	4.853%	$82.7919	$82.79	$82.80	$82.80
Purchase #7	$56.46	13.479%	$64.0702	$64.07	$64.05	$64.10
7 purchase totals =	$598.54		$660.5032	$660.50	$660.50	$660.50