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	$114.61	5.482%	$120.8929	$120.89	$120.90	$120.90
Purchase #2	$8.47	9.839%	$9.3034	$9.30	$9.30	$9.30
Purchase #3	$213.32	11.529%	$237.9137	$237.91	$237.90	$237.90
Purchase #4	$67.93	3.670%	$70.423	$70.42	$70.40	$70.40
Purchase #5	$31.42	3.865%	$32.6344	$32.63	$32.65	$32.60
Purchase #6	$82.68	8.275%	$89.5218	$89.52	$89.50	$89.50
Purchase #7	$110.39	10.444%	$121.9191	$121.92	$121.90	$121.90
7 purchase totals =	$628.82		$682.6083	$682.59	$682.55	$682.50