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	$41.86	9.383%	$45.7877	$45.79	$45.80	$45.80
Purchase #2	$245.62	10.321%	$270.9704	$270.97	$270.95	$271.00
Purchase #3	$141.31	5.323%	$148.8319	$148.83	$148.85	$148.80
Purchase #4	$135.91	9.261%	$148.4966	$148.50	$148.50	$148.50
Purchase #5	$157.43	4.503%	$164.5191	$164.52	$164.50	$164.50
Purchase #6	$38.87	3.506%	$40.2328	$40.23	$40.25	$40.20
Purchase #7	$90.31	12.140%	$101.2736	$101.27	$101.25	$101.30
7 purchase totals =	$851.31		$920.1121	$920.11	$920.10	$920.10