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	$235.73	5.229%	$248.0563	$248.06	$248.05	$248.10
Purchase #2	$75.51	9.177%	$82.4396	$82.44	$82.45	$82.40
Purchase #3	$72.34	12.182%	$81.1525	$81.15	$81.15	$81.20
Purchase #4	$122.47	9.598%	$134.2247	$134.22	$134.20	$134.20
Purchase #5	$94.90	3.843%	$98.547	$98.55	$98.55	$98.50
Purchase #6	$205.53	8.178%	$222.3382	$222.34	$222.35	$222.30
Purchase #7	$107.57	3.649%	$111.4952	$111.50	$111.50	$111.50
7 purchase totals =	$914.05		$978.2535	$978.26	$978.25	$978.20