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	$164.49	4.684%	$172.1947	$172.19	$172.20	$172.20
Purchase #2	$225.44	9.280%	$246.3608	$246.36	$246.35	$246.40
Purchase #3	$52.60	4.799%	$55.1243	$55.12	$55.10	$55.10
Purchase #4	$199.48	5.396%	$210.2439	$210.24	$210.25	$210.20
Purchase #5	$96.81	7.302%	$103.8791	$103.88	$103.90	$103.90
Purchase #6	$42.30	9.711%	$46.4078	$46.41	$46.40	$46.40
Purchase #7	$208.92	10.773%	$231.427	$231.43	$231.45	$231.40
7 purchase totals =	$990.04		$1,065.6376	$1,065.63	$1,065.65	$1,065.60