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	$53.64	3.654%	$55.6	$55.60	$55.60	$55.60
Purchase #2	$233.34	12.842%	$263.3055	$263.31	$263.30	$263.30
Purchase #3	$128.75	5.765%	$136.1724	$136.17	$136.15	$136.20
Purchase #4	$118.68	11.738%	$132.6107	$132.61	$132.60	$132.60
Purchase #5	$165.50	11.865%	$185.1366	$185.14	$185.15	$185.10
Purchase #6	$195.90	10.681%	$216.8241	$216.82	$216.80	$216.80
Purchase #7	$80.39	10.642%	$88.9451	$88.95	$88.95	$88.90
7 purchase totals =	$976.20		$1,078.5944	$1,078.60	$1,078.55	$1,078.50