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	$42.34	9.827%	$46.5008	$46.50	$46.50	$46.50
Purchase #2	$152.47	10.394%	$168.3177	$168.32	$168.30	$168.30
Purchase #3	$128.50	5.255%	$135.2527	$135.25	$135.25	$135.30
Purchase #4	$225.43	10.501%	$249.1024	$249.10	$249.10	$249.10
Purchase #5	$127.25	12.828%	$143.5736	$143.57	$143.55	$143.60
Purchase #6	$26.55	4.649%	$27.7843	$27.78	$27.80	$27.80
Purchase #7	$55.41	12.445%	$62.3058	$62.31	$62.30	$62.30
7 purchase totals =	$757.95		$832.8373	$832.83	$832.80	$832.90