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	$233.44	3.236%	$240.9941	$240.99	$241.00	$241.00
Purchase #2	$38.72	6.829%	$41.3642	$41.36	$41.35	$41.40
Purchase #3	$76.25	3.453%	$78.8829	$78.88	$78.90	$78.90
Purchase #4	$14.34	6.753%	$15.3084	$15.31	$15.30	$15.30
Purchase #5	$97.97	11.351%	$109.0906	$109.09	$109.10	$109.10
Purchase #6	$65.69	6.730%	$70.1109	$70.11	$70.10	$70.10
Purchase #7	$43.42	9.111%	$47.376	$47.38	$47.40	$47.40
7 purchase totals =	$569.83		$603.1271	$603.12	$603.15	$603.20