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	$83.97	6.600%	$89.512	$89.51	$89.50	$89.50
Purchase #2	$141.41	6.398%	$150.4574	$150.46	$150.45	$150.50
Purchase #3	$85.27	12.617%	$96.0285	$96.03	$96.05	$96.00
Purchase #4	$166.53	11.261%	$185.2829	$185.28	$185.30	$185.30
Purchase #5	$59.83	10.853%	$66.3233	$66.32	$66.30	$66.30
Purchase #6	$191.73	6.102%	$203.4294	$203.43	$203.45	$203.40
Purchase #7	$185.85	7.630%	$200.0304	$200.03	$200.05	$200.00
7 purchase totals =	$914.59		$991.0639	$991.06	$991.10	$991.00