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	$7.48	11.786%	$8.3616	$8.36	$8.35	$8.40
Purchase #2	$106.41	9.366%	$116.3764	$116.38	$116.40	$116.40
Purchase #3	$59.84	13.445%	$67.8855	$67.89	$67.90	$67.90
Purchase #4	$33.95	12.278%	$38.1184	$38.12	$38.10	$38.10
Purchase #5	$225.34	12.478%	$253.4579	$253.46	$253.45	$253.50
Purchase #6	$40.80	10.607%	$45.1277	$45.13	$45.15	$45.10
Purchase #7	$97.33	4.480%	$101.6904	$101.69	$101.70	$101.70
7 purchase totals =	$571.15		$631.0179	$631.03	$631.05	$631.10