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	$40.82	6.282%	$43.3843	$43.38	$43.40	$43.40
Purchase #2	$122.89	10.301%	$135.5489	$135.55	$135.55	$135.50
Purchase #3	$63.76	12.433%	$71.6873	$71.69	$71.70	$71.70
Purchase #4	$40.36	6.631%	$43.0363	$43.04	$43.05	$43.00
Purchase #5	$39.35	3.470%	$40.7154	$40.72	$40.70	$40.70
Purchase #6	$43.61	9.735%	$47.8554	$47.86	$47.85	$47.90
Purchase #7	$41.52	10.637%	$45.9365	$45.94	$45.95	$45.90
7 purchase totals =	$392.31		$428.1641	$428.18	$428.20	$428.10