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	$73.96	11.545%	$82.4987	$82.50	$82.50	$82.50
Purchase #2	$63.50	10.110%	$69.9199	$69.92	$69.90	$69.90
Purchase #3	$36.36	5.789%	$38.4649	$38.46	$38.45	$38.50
Purchase #4	$134.93	5.710%	$142.6345	$142.63	$142.65	$142.60
Purchase #5	$173.32	5.621%	$183.0623	$183.06	$183.05	$183.10
Purchase #6	$161.66	11.379%	$180.0553	$180.06	$180.05	$180.10
Purchase #7	$131.44	12.227%	$147.5112	$147.51	$147.50	$147.50
7 purchase totals =	$775.17		$844.1468	$844.14	$844.10	$844.20