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	$201.37	3.531%	$208.4804	$208.48	$208.50	$208.50
Purchase #2	$89.59	12.419%	$100.7162	$100.72	$100.70	$100.70
Purchase #3	$157.38	13.419%	$178.4988	$178.50	$178.50	$178.50
Purchase #4	$161.79	6.749%	$172.7092	$172.71	$172.70	$172.70
Purchase #5	$230.84	7.810%	$248.8686	$248.87	$248.85	$248.90
Purchase #6	$222.92	10.132%	$245.5063	$245.51	$245.50	$245.50
Purchase #7	$119.63	12.454%	$134.5287	$134.53	$134.55	$134.50
7 purchase totals =	$1,183.52		$1,289.3082	$1,289.32	$1,289.30	$1,289.30