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	$77.69	6.223%	$82.5246	$82.52	$82.50	$82.50
Purchase #2	$187.39	9.288%	$204.7948	$204.79	$204.80	$204.80
Purchase #3	$183.50	5.663%	$193.8916	$193.89	$193.90	$193.90
Purchase #4	$107.93	8.652%	$117.2681	$117.27	$117.25	$117.30
Purchase #5	$98.59	13.354%	$111.7557	$111.76	$111.75	$111.80
Purchase #6	$236.34	7.702%	$254.5429	$254.54	$254.55	$254.50
Purchase #7	$205.67	9.599%	$225.4123	$225.41	$225.40	$225.40
7 purchase totals =	$1,097.11		$1,190.1900	$1,190.18	$1,190.15	$1,190.20