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	$125.34	9.817%	$137.6446	$137.64	$137.65	$137.60
Purchase #2	$167.92	10.162%	$184.984	$184.98	$185.00	$185.00
Purchase #3	$128.75	10.819%	$142.6795	$142.68	$142.70	$142.70
Purchase #4	$88.47	9.333%	$96.7269	$96.73	$96.75	$96.70
Purchase #5	$249.32	7.590%	$268.2434	$268.24	$268.25	$268.20
Purchase #6	$78.49	7.357%	$84.2645	$84.26	$84.25	$84.30
Purchase #7	$174.59	6.359%	$185.6922	$185.69	$185.70	$185.70
7 purchase totals =	$1,012.88		$1,100.2351	$1,100.22	$1,100.30	$1,100.20